SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                   ----------

                                    FORM 8-K

                                   ----------

                                 CURRENT REPORT
                     PURSUANT TO SECTION 13 OR 15(D) OF THE
                         SECURITIES EXCHANGE ACT OF 1934

Date of Report (Date of earliest event reported)           October 1, 1997
                                                     -------------------------


                          ALEXION PHARMACEUTICALS, INC.
- --------------------------------------------------------------------------------
             (Exact Name of Registrant as Specified in its Charter)

        Delaware                         0-27756                13-3648318
- ----------------------------          ------------           -------------------
(State or Other Jurisdiction          (Commission               (IRS Employer
     of Incorporation)                File Number)           Identification No.)

 
     25 Science Park, New Haven, CT                                06511
- ---------------------------------------                          ----------
(Address of Principal Executive Offices)                         (Zip Code)


Registrant's telephone number, including area code:       (203) 776-1790
                                                       ----------------------


                                 Not Applicable
- --------------------------------------------------------------------------------
          (Former Name or Former Address, if Changed Since Last Report)





ITEM 5.  OTHER EVENTS

     On October 1, 1997, Alexion Pharmaceuticals, Inc. issued the press release
filed herewith as Exhibit 99.

ITEM 7.  FINANCIAL STATEMENTS, PRO FORMA FINANCIAL INFORMATION AND EXHIBITS.

     (C) EXHIBITS.

     10.1 Amendment to Joint Development Agreement dated as of September 30,
1997 by and between the Company and United States Surgical Corporation.+

     10.2 Stock Purchase Agreement dated September 30, 1997 by and between the
Company and United States Surgical Corporation.+

     99. Press Release dated October 1, 1997.

- ----------------

+ A request for confidential treatment will be made for portions of such
document. Confidential portions have been omitted and will be filed separately
with the Commission as required by Rule 24b-2 under the Securities Exchange Act
of 1934, as amended.





                                   SIGNATURES

     Pursuant to the requirements of the Securities Exchange Act of 1934, the
registrant has duly caused this report to be signed on its behalf by the
undersigned hereunto duly authorized.

                                          ALEXION PHARMACEUTICALS, INC.

Date: October 1, 1997                     By: \s\ LEONARD BELL
                                              ----------------------------------
                                              Name:  Leonard Bell, M.D.
                                              Title: President, Chief Executive
                                                     Officer, Secretary and
                                                     Treasurer


[Confidential treatment has been requested for portions of this exhibit. The
confidential portions have been redacted and are denoted by [______________].
The confidential portions have been separately filed with the commission.]



                   AMENDMENT TO JOINT DEVELOPMENT AGREEMENT

      This AMENDMENT TO JOINT DEVELOPMENT AGREEMENT (this "Agreement") is made
as of September 30, 1997 by and between ALEXION PHARMACEUTICALS, INC., a
Delaware corporation ("Alexion"), having its principal place of business at 25
Science Park, Suite 360, New Haven, Connecticut 06511, and UNITED STATES
SURGICAL CORPORATION, a Delaware Corporation ("USSC"), having its principal
place of business at 150 Glover Avenue, Norwalk, Connecticut 06856.

                                   Background

      A. Alexion and USSC entered into a Joint Development Agreement dated as of
July 31, 1995 (the "Original Agreement"), pursuant to which Alexion and USSC
established a cooperative arrangement for the development and commercialization
of certain proprietary technology of Alexion relating to [________________].
(Capitalized terms not otherwise defined herein have the meaning given in the
Original Agreement.)

      B. In view of (i) the substantial progress made by Alexion toward certain
milestones in the Original Agreement and (ii) certain inventions acquired by
Alexion that may have application in the Field, USSC desires to (a) recognize
Alexion's research and pre-clinical progress by increasing USSC's investment in
Alexion on the terms and conditions set forth in a certain Share Purchase
Agreement being entered into contemporaneously with this Agreement and (b)
obtain exclusive rights to such inventions in the Field, and Alexion and USSC
wish to modify the Original Agreement as set forth below.

      In consideration of the premises and of other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged, the
parties agree as follows:

      1.    Pre-Clinical Funding

            1.1 Subsection 3.4(c)of the Original Agreement is hereby amended by
deleting clauses 3.4(c)(i)(B) and 3.4(c)(ii) in their entirety.




            1.2 Subsection 3.4(d) of the Original Agreement is hereby amended by
inserting the following sentence at the beginning of such paragraph: "It is
agreed that two important milestones are the attainment of the DC/HT Milestone
and the Primate Milestone," and by deleting from the first sentence thereof the
phrase "make the payment associated with such milestone or."

      2.    Amendment of License to Include New Patent Application; Certain
Pigs

            2.1 The parties wish to confirm that "Alexion Transplantation
Technology Invention" shall include the invention described in the New Patent
Application (as defined below), which invention shall hereafter be deemed to be
within the scope of the license with respect to Alexion Transplantation
Technology Inventions granted to USSC pursuant to Section 3.5(h) of the Original
Agreement.

            2.2 The Disclosure Schedule appended to the Original Agreement is
hereby amended by adding as Patent No. 20. disclosed thereon, the following
patent application and all patents which issue thereon and foreign counterparts
thereof, any continuations, continuations-in-part, divisions, reissues,
reexaminations, additions and renewals of any such applications or patents
(collectively, the "New Patent Application"):

            "20.  [___________________________________________]

            2.3 (a) Notwithstanding the provisions of the Section 6.2 of the
Original Agreement, transgenic pigs produced both (i) under the license to the
New Patent Application granted pursuant to Section 2.2 of this Agreement and
(ii) during the performance of the Research and Development Programs under the
Original Agreement shall be owned by USSC ("USSC Pigs"), with the exclusive
worldwide marketing, sales and distribution rights for the USSC Pigs, subject to
the reservation and retention by Alexion of an undivided co-ownership interest
in all [__________] ("[ ]Constituents"), and the perpetual, royalty-free,
non-transferable right and license to practice all technology of Alexion or in
which it has an interest which may be included in the USSC Pigs for research
purposes, only on a non-commercial basis, and subject to the other provisions of
this Section 2.3.

                                       2


            (b) USSC's rights to use the USSC Pigs (including [____________]
Constituents) shall be limited to the Field, and by the scope, duration and any
other limitations on USSC's rights to use Transplantation Technology or sell
Products or which is otherwise applicable pursuant to the Original Agreement,
including the licenses granted to USSC with respect to the New Patent
Application.

            (c) Alexion shall own the exclusive, worldwide right, with the right
of assignment or license, to make, have made, use and sell transgenic pigs
(other than USSC Pigs) produced under the New Patent Application outside the
Field. Alexion shall have no duty to seek the consent or approval of USSC, nor
to account to USSC, for use of [_____________] Constituents outside the Field or
pursuant to the research license reserved by Alexion. USSC and Alexion each
hereby waives any rights it may now or hereafter have with respect to partition.

            (d) USSC shall, at any time and from time to time, upon reasonable
notice and during normal business hours, provide Alexion with
[_____________________], for the purpose of allowing Alexion
[____________________________________] as Alexion may reasonably require.
[___________________________________________]

            2.4 (a) All terms defined in the Original Agreement based on or
incorporating, directly or indirectly, the term specified below shall be deemed
modified as follows:

                        (i) Alexion Transplantation Technology Invention,
including without limitation, the terms Products, Transplantation Technology and
Net Sales, shall be deemed modified to the extent necessary to include the New
Patent Application, and

                        (ii) Products, including without limitation, the term
Net Sales, shall be deemed modified to the extent necessary to include USSC Pigs
and [____________] Constituents.

            (b) The provisions of Section 3.5(n) of the Original Agreement shall
be applicable to transfers or licenses by USSC of rights to USSC Pigs or
[___________] Constituents as if same were Products, and the provisions of
Section 6.4 of the Original Agreement shall set forth the allocation of patent
prosecution

                                       3



and litigation responsibilities for USSC Pigs (including Germline Constituents).

            2.5 The rights granted to USSC in this Agreement with respect to the
USSC Pigs and [______________] Constituents shall not be construed to confer any
rights upon USSC by implication, estoppel or otherwise as to any technology
licensed to USSC pursuant to the Original Agreement, including the New Patent
Application, or any technology not specifically identified in this Agreement as
or included within such rights, and no other assignments or licenses are made or
granted by implication, estoppel or otherwise, by this Agreement.

            2.6 The parties acknowledge and agree that the invention described
in the New Patent Application or a portion thereof, including technology to
create USSC Pigs, was developed with financial or other assistance from the
United States of America, and that applicable statutes, regulations and
Executive Orders of the United States of America may control, apply to or affect
USSC's rights to such technology. Without limiting the foregoing, such license
to, conveyance of, and the rights thereunder of, USSC shall be, with respect to
the New Patent Application and USSC Pigs (including [_______________________]
Constituents), subject to the license and other rights granted to and reserved
by the United States Government pursuant to Section 11 of the General Terms and
Conditions to that certain Advanced Technology Program, Cooperative Agreement
[____________________________________________________________________].

            2.7 Subject to Section 2.6 of this Agreement, Alexion hereby makes
and repeats the representations and warranties set forth in Section 8.1 of the
Original Agreement with respect to this Agreement, the New Patent Application
and the USSC Pigs, all of which are true and correct with respect thereto.
ALEXION ALSO HEREBY MAKES AND REPEATS THE EXCLUSIONS AND LIMITATIONS SET FORTH
IN SECTIONS 9.4 AND 9.5 OF THE ORIGINAL AGREEMENT AS SUCH EXCLUSIONS AND
LIMITATIONS PERTAIN TO USSC PIGS (INCLUDING [______________] CONSTITUENTS).

      3. Additional Payment.

            3.1 Upon the execution hereof, USSC shall pay to Alexion $3,500,000
(the "Additional Payment") by wire transfer in

                                       4




good funds in accordance with wire transfer instructions previously provided by
Alexion to USSC.

            3.2 The Additional Payment shall be a one-time, non- refundable fee
paid by USSC in consideration for Alexion's grant of the foregoing license with
regard to the New Patent Application and rights with regard to USSC Pigs. Such
payment shall not be credited against any royalty payable under Section 3.5(i)
of the Original Agreement or any other amount payable by USSC to Alexion.

       4. Effect of this Amendment. Except as expressly amended or modified
hereby, the Original Agreement shall remain in full force and effect.

            The parties have caused this Agreement to be signed by their
respective officers as of the date first written above.

                                    ALEXION PHARMACEUTICALS, INC.

                                    By: /s/ DAVID KEISER
                                       ----------------------------------------
                                       Name: David Keiser
                                       Title: Exec VP & COO

                                    UNITED STATES SURGICAL CORPORATION

                                    By: /s/ RICHARD A. DOUVILLE
                                       ----------------------------------------
                                       Name: Richard A. Douville
                                       Title:   Senior Vice President


                                       5


[Confidential treatment has been requested for portions of this exhibit. The
confidential portions have been redacted and are denoted by [______________].
The confidential portions have been separately filed with the commission.]


                            STOCK PURCHASE AGREEMENT

Alexion Pharmaceuticals, Inc.
25 Science Park
New Haven, CT 06511

Ladies & Gentlemen:

      The undersigned, United States Surgical Corporation, a Delaware
corporation (the "Investor"), hereby confirms its agreement with you as follows:

      1. This Stock Purchase Agreement (the "Agreement") is made as of September
29, 1997 between Alexion Pharmaceuticals, Inc., a Delaware corporation (the
"Company"), and the Investor.

      2. The Company has authorized the sale and issuance of that number of
shares of the Company's Common Stock, par value $.0001 per share (the "Common
Stock"), obtained by dividing 3,000,000 by a purchase price per share (the
"Price Per Share") equal to 125% of the closing price of the Common Stock on the
Nasdaq National Market reported for the trading day immediately preceding the
Closing Date (as defined below), for an aggregate purchase price (the "Purchase
Price") of Three Million Dollars ($3,000,000). The shares of Common Stock being
sold under this Agreement are referred to as the "Shares."

      3. The Company and the Investor agree that the Investor will purchase and
the Company will sell, for the Price Per Share, or an aggregate Purchase Price
of $3,000,000.00, the Shares, and upon such purchase and sale, the Company will
issue the Shares, pursuant to the Terms and Conditions for Purchase of Shares
attached hereto as Annex I and incorporated herein by this reference as if fully
set forth herein (any reference to the "Agreement" in Annex I shall mean this
signature page and Annex I hereto, collectively). Unless otherwise requested by
the Investor, certificates representing the Shares will be registered in the
Investor's name and address as set forth below.





      Please confirm that the foregoing correctly sets forth the agreement
between us by signing in the space below for that purpose.

                              INVESTOR:

                              UNITED STATES SURGICAL CORPORATION

                              By: /s/ Richard A. Douville
                                 ----------------------------------------------
                              Title: Senior Vice President and Chief
                                       Financial Officer

                              Address: 150 Glover Avenue
                                       Norwalk, Connecticut 06856

                              Tax ID No.:      132518270
                                          -----------------------------
                              Contact name: Richard A. Douville, Senior
                              Vice President and Chief Financial Officer

                              Telephone: (203) 845-4446

Name in which the Shares should be registered (if different):

                              --------------------------------------



AGREED AND ACCEPTED:

ALEXION PHARMACEUTICALS, INC.

    /s/ DAVID W. KEISER
- ------------------------------------
By: David W. Keiser,
    Executive Vice Presidnet and Chief Operating Offier

                                       2



                                     ANNEX I

                 TERMS AND CONDITIONS FOR PURCHASE OF SHARES

      1. Authorization and Sale of the Shares. Subject to the terms and
conditions of this Agreement, the Company has authorized the sale and issuance
of the Shares for the Price Per Share and for the aggregate Purchase Price.

      2. Agreement to Sell and Purchase the Shares. At the Closing (as defined
in Section 3), the Company will sell to the Investor, and the Investor will
purchase from the Company, upon the terms and conditions hereinafter set forth,
the Shares at the Price Per Share and the Purchase Price.

      3. Delivery of the Shares at Closing. The completion of the purchase and
sale of the Shares (the "Closing") shall occur on September 29, 1997 (the
"Closing Date"). At the Closing, the Company shall deliver to the Investor one
or more stock certificates representing the Shares, each such certificate to be
registered in the name of the Investor or, if so indicated on the signature page
hereto, in the name of a nominee designated by the Investor.

      The Company's obligation to close the transaction shall be subject to the
following conditions, any one or more of which may be waived by the Company: (a)
receipt by the Company of a certified or official bank check or wire transfer of
funds in the full amount of the purchase price for the Shares; (b) the accuracy
of the representations and warranties made by the Investor and the fulfillment
of those undertakings of the Investor to be fulfilled prior to the Closing, and
(c) the Investor's execution and delivery to the Company of that certain
Amendment to Joint Development Agreement between the Company and the Investor
dated as of the Closing Date (the "Amendment to Joint Development Agreement")
substantially in the form of Exhibit A hereto.

      The Investor's obligation to close the transaction shall be subject to:
(a) the receipt of the Shares; (b) receipt of a certificate of the Company's
Chief Financial Officer or any Vice President as to the determination of the
Price Per Share and the Purchase Price; (c) the accuracy of the representations
and warranties made by the Company and the fulfillment of those

                                       3


undertakings of the Company to be fulfilled prior to the Closing; and (d) the
Company's execution and delivery to the Investor of the Amendment to Joint
Development Agreement.

      4. Representations, Warranties and Covenants of the Company. The Company
hereby represents and warrants to, and covenants with, the Investor as follows:

      4.1. Organization. The Company is a corporation duly organized, validly
existing and in good standing under the laws of the State of Delaware. The
Company has all requisite corporate power and corporate authority to own,
operate and occupy its properties and conduct its business as presently
conducted and as described in its Annual Report on Form 10-K for the year ended
July 31, 1996 (the "10-K")and the Company's Quarterly Report on Form 10-Q for
the fiscal quarter ended October 31, 1996, the Company's Quarterly Report on
Form 10-Q for the fiscal quarter ended January 31, 1997, as amended by Form
10-Q/A, filed March 17, 1997, and Form 10-Q/A2, filed June 19, 1997, the
Company's Quarterly Report on Form 10-Q for the fiscal quarter ended April 30,
1997, the Company's Current Report on Form 8-K, dated February 28, 1997, the
Company's Current Report on Form 8-K, dated June 17, 1997, the Company's Current
Report on Form 8-K dated July 9, 1997, the Company's Current Report on Form 8-K
dated September 10, 1997, the Company's Registration Statement on Form 8-A dated
February 21, 1997 and its Registration Statements on Form S-3 dated July 7, 1997
and July 18, 1997, respectively, the foregoing filings constitute all documents
filed by the Company since the date of the 10-K with the Securities and Exchange
Commission (the "SEC") under the Securities Exchange Act of 1934, as amended
(the "Exchange Act")(all such documents are hereinafter referred to as the "1934
Act Filings"), and the Company is registered or qualified to do business and in
good standing in each jurisdiction in which it owns or leases property or
transacts business and where the failure to be so qualified would have a
material adverse effect upon the business, financial condition, properties or
operations of the Company. The Company has no subsidiaries.

      4.2. Due Authorization. The Company has all requisite corporate power and
corporate authority to execute, deliver and perform its obligations under this
Agreement and the Amendment to Joint Development Agreement and each of this
Agreement and the Amendment to Joint Development Agreement has been duly
authorized 

                                       4


and validly executed and delivered by the Company and constitutes the legal,
valid and binding agreement of the Company enforceable against the Company in
accordance with its terms, except as rights to indemnity and contribution may be
limited by state or federal securities laws or the public policy underlying such
laws, except as enforceability may be limited by applicable bankruptcy,
insolvency, reorganization, moratorium or similar laws affecting creditors' and
contracting parties' rights generally and except as enforceability may be
subject to general principles of equity (regardless of whether such
enforceability is considered in a proceeding in equity or at law).

      4.3. Issuance of Shares. The issuance, sale and delivery of the Shares in
accordance with this Agreement have been duly authorized by all required
corporate action on the part of the Company, and the Shares, when issued, sold,
and delivered in accordance with the terms hereof for the consideration
expressed herein, will be duly and validly issued, fully paid and non-assessable
and, based upon the representations and warranties of the Investor in this
Agreement, will be issued in compliance with all applicable federal and state
securities laws. The Shares issued hereunder will be free and clear from any
liens or encumbrances other than those created by, or imposed upon, the holders
thereof through no action of the Company; provided, that such Shares may be
subject to restrictions on transfer under state and/or federal securities laws
as set forth herein. The issuance of the Shares will not cause any anti-dilution
or preemptive rights provisions contained in any material agreement of the
Company to become operative.

      4.4. Non-Contravention. The execution and delivery of this Agreement and
the Amendment to Joint Development Agreement, the issuance and sale of the
Shares to be sold by the Company hereunder, the performance of the terms of this
Agreement and the Amendment to Joint Development Agreement and the consummation
of the transactions contemplated hereby and thereby will not conflict with or
constitute a violation of, or default (with the passage of time or otherwise)
under, any material agreement or instrument to which the Company is a party or
by which it is bound or the charter, by-laws or other organizational documents
of the Company nor result in the creation or imposition of any lien,
encumbrance, claim, security interest or restriction whatsoever upon any of the
material properties or assets of the Company or an acceleration of indebtedness
pursuant to any 


                                       5



obligation, agreement or condition contained in any material bond, debenture,
note or any other evidence of indebtedness or any material indenture, mortgage,
deed of trust or any other agreement or instrument to which the Company is a
party or by which it is bound or to which any of the property or assets of the
Company is subject, or conflict with, or result in a violation of, any law,
administrative regulation, ordinance, order, judgment or decree of any court or
governmental agency, arbitration panel or authority applicable to the Company.
No consent, approval, authorization or other order of, or registration,
qualification or filing with, any regulatory body, administrative agency, or
other governmental body in the United States is required for the valid issuance
and sale of the Shares, other than such as have been made or obtained before the
date of this Agreement, and other than a Form D which will be filed under the
Securities Act of 1933, as amended (the "Securities Act"), after the Closing
Date.

      4.5. Capitalization. The capitalization of the Company as of July 31, 1996
is as set forth in the 10-K. The Company has not issued any capital stock since
that date other than as contemplated by or described in the 1934 Act Filings,
including the issuance in June 1997 of 1,450,000 shares of Common Stock in a
private placement transaction and the issuance on September 15, 1997 of 400,000
shares of Series B Convertible Preferred Stock, par value $.0001 per share (the
"Series B Preferred Stock"). At September 15, 1997 the Company had outstanding
9,805,625 shares of Common Stock (assuming conversion of all shares of Series B
Convertible Stock), holds in treasury 11,875 shares of Common Stock and has
outstanding options and warrants to purchase 1,467,109 and 926,669 shares of
Common Stock, respectively. All outstanding shares of capital stock of the
Company have been duly and validly issued and are fully paid and nonassessable.
Except as set forth above, or as described in the 1934 Act Filings, as of
September 15, 1997, there are no outstanding rights (including, without
limitation, preemptive rights), warrants or options to acquire, or instruments
convertible into or exchangeable for, any shares of capital stock or other
equity interest in the Company, or any contract, commitment, agreement,
understanding or arrangement of any kind relating to the issuance of any capital
stock of the Company, any such convertible or exchangeable securities or any
such rights, warrants or options.

      4.6. Legal Proceedings. There is no material legal or 


                                       6



governmental proceeding pending or, to the knowledge of the Company, threatened
or contemplated to which the Company is or may be a party or of which the
business or property of the Company is or may be subject that is not disclosed
in the 1934 Act Filings, and to the Company's knowledge no basis exists for any
(i) legal proceeding by or against the Company or (ii) governmental proceeding
or investigation of the Company.

      4.7. No Violations. The Company is not (a) in violation of its certificate
of incorporation or bylaws, or of any law, administrative regulation, ordinance,
order, judgment or decree of any court or governmental agency, arbitration panel
or authority applicable to the Company, or (b) in default in any respect in the
performance of any obligation, agreement or condition contained in any bond,
debenture, note or any other evidence of indebtedness or in any indenture,
mortgage, deed of trust or any other agreement or instrument to which the
Company is a party or by which the Company is bound or by which the properties
of the Company are bound or affected, and there exists no condition which, with
the passage of time or otherwise, would constitute a default under any such
agreement, document or instrument or result in the imposition of any penalty or
the acceleration of any indebtedness, except for any such violation, default,
penalty or acceleration which, individually or in the aggregate, would not have
a material adverse effect on the business or financial condition of the Company.

      4.8. Required Permits, Etc. The Company has all franchises, permits,
licenses and any similar authority necessary for the conduct of its business now
being conducted by it, the lack of which could materially and adversely affect
the business, properties, or financial condition of the Company, and the Company
believes it can obtain, without undue burden or expense, any similar authority
for the conduct of its business as proposed to be conducted. The Company is not
in default in any material respect under any such franchise, permit, license or
other similar authority.

      4.9. Intellectual Property. The Company will take reasonable security
measures in the future, as it presently is doing, to protect the secrecy,
confidentiality, and value of all of its trade secrets, know-how, inventions,
prototypes, designs, processes, and technical data important to the conduct of
its business. Except as described in the 1934 Act Filings, the 

                                       7




Company owns or possesses sufficient rights to use all material patents, patent
rights, trademarks, copyrights, licenses, inventions, trade secrets and know-how
described or referred to in the 1934 Act Filings as owned or used by it
necessary for the conduct of its business as now conducted. Except as described
in the 1934 Act Filings, the Company has not received any notice of, and has no
knowledge of or reason to believe that, any infringement of or conflict with any
right of others with respect to any patent, patent right, trademark, copyright,
invention, trade secret or know-how that, individually or in the aggregate would
have a material adverse effect on the condition (financial or otherwise),
earnings, operations, business or business prospects of the Company. Except as
described in the 1934 Act Filings, the Company has not entered into or become
party to any material development, work for hire, license or other agreement
[_____________________] pursuant to which the Company has secured the right or
obligation to use, or granted others the right or obligation to use, any
material trademarks, servicemarks, trade names, copyrights, patents or any other
material intellectual property right in [_______________________]

      4.10. Financial Statements. The financial statements of the Company and
the related notes contained in the 1934 Act Filings present fairly, subject to
customary year-end adjustments in the case of the quarterly statements, the
financial position of the Company as of the dates indicated, and the results of
its operations and cash flows for the periods therein specified and the assets
and liabilities of the Company have not changed significantly since the date of
the most recent 1934 Act Filing, except for changes in the ordinary course of
business or resulting from the Company's private placement of Common Stock
during June 1997 and from the Company's private placement of Series B Preferred
Stock in September 1997. Such financial statements (including the related notes)
have been prepared in accordance with generally accepted accounting principles
applied on a consistent basis throughout the periods therein specified, except
as disclosed in the 1934 Act Filings. The other financial information contained
in the 1934 Act Filings has been prepared on a basis consistent with the
financial statements of the Company.

      4.11. No Material Adverse Change. Subsequent to the respective dates as of
which information is given in the 1934 Act Filings, and except as contemplated
or described in the 1934 Act 

                                       8


Filings, the Company has not incurred any material liabilities or obligations,
direct or contingent, other than in the ordinary course of business, and there
has not been any material adverse change in its condition (financial or other),
results of operations, business, prospects, key personnel or capitalization, it
being understood that the Company has continued to use working capital to fund
operations without significant contributions from revenues.

      4.12. Additional Information. The Company has filed in a timely manner all
documents that the Company was required to file under the Exchange Act since the
Company's initial public offering. The 1934 Act Filings complied in all material
respects with the SEC's requirements as of their respective filing dates, and
the information contained therein as of the respective dates thereof did not
contain any untrue statement of material fact or omit to state any material fact
required to be stated therein or necessary to make the statements therein not
misleading.

      4.13. Title to Property and Assets. Except as described in the 1934 Act
Filings, the Company has good and valid title to its property and assets, free
and clear of all mortgages, liens, loans, and encumbrances, except such
encumbrances and liens which arise in the ordinary course of business and do not
materially impair the Company's ownership or use of such property or assets.
With respect to the property and assets it leases, the Company is in compliance
with such leases and, to its knowledge, holds a valid leasehold interest free of
any liens, claims, or encumbrances. All of the Company's tangible properties and
assets are, in all material respects, in good operating and usable condition,
subject to normal wear and tear.

      4.14. Environmental Matters. The Company is in compliance in all respects
with all applicable local, state and federal safety and environmental laws,
rules, orders and regulations ("Environmental Laws") under the jurisdiction of
the USDA, BATF, USNRC and CTDEP and any other federal or state agency with
applicable programs relating to biosafety, chemical hygiene, radiation safety,
blood borne pathogens, hazard communication, hazardous waste management and
chemical, medical and radiation waste disposal, except where the failure to
comply with the Environmental Laws will not have a material adverse effect upon
the business or financial condition of the Company.

                                       9


      4.15. Reliance. The Company acknowledges that the Investor has reviewed
and relied upon the 1934 Act Filings in making its decision to purchase the
Shares.

      5. Representations, Warranties and Covenants of the Investor.

      a) The Investor represents and warrants to, and covenants with, the
Company that: (i) the Investor is an "accredited investor" as defined in
Regulation D under the Securities Act and the Investor is also knowledgeable,
sophisticated and experienced in making, and is qualified to make decisions with
respect to investments in securities presenting an investment decision like that
involved in the purchase of the Shares, including investments in securities
issued by the Company and investments in comparable companies; (ii) the Investor
has been given the opportunity to ask questions of, and receive answers from, a
qualified representative of the Company concerning the terms and conditions of
this offering, the business and financial condition of the Company and other
matters pertaining to this investment, and has been given the opportunity to
obtain such other information necessary to evaluate the merits and risks of an
investment in the Shares as the Investor deems necessary, and the Investor has
received, reviewed and considered the "RISK FACTORS" attached as Exhibit B
hereto; (iii) the Investor is not relying on the Company with respect to any
economic considerations involved in the investment in the Shares, and no
representations or warranties, other than as set forth in Section 4 herein, have
been made to the Investor by the Company or any officer, employee, agent or
affiliate of the Company; (iv) the Investor is acquiring the Shares for
investment for its own account, not as a nominee or agent, and not with a view
to the resale or distribution of any part thereof, and the Investor has no
present intention of selling, granting any participation in, or otherwise
distributing the same; and (v) the Investor will not, directly or indirectly,
sell, offer to sell, loan, grant any right to, pledge, transfer or otherwise
dispose of (or solicit any offers to buy, purchase or otherwise acquire or take
a pledge of)(collectively, a "disposition") any of the Shares except in
compliance with the Securities Act, applicable state securities laws and the
respective rules and regulations promulgated thereunder.

      b) The Investor understands that the Shares are "restricted 

                                       10




securities" under the federal securities laws inasmuch as they are being
acquired from the Company in a transaction not involving a public offering and
that under such laws and applicable regulations such securities may be resold
without registration under the Securities Act only in certain limited
circumstances. In this regard, the Investor represents that it is familiar with
SEC Rule 144 ("Rule 144"), as presently in effect, and understands the resale
limitations imposed thereby and by the Securities Act. The Investor is prepared
to hold the Shares for an indefinite period of time.

      c) Without in any way limiting the representations set forth above, the
Investor further agrees not to make any disposition of all or any portion of the
Shares unless (i) there is then in effect a registration statement under the
Securities Act covering such proposed disposition and such disposition is made
in accordance with such registration statement, or (ii) the Investor shall have
notified the Company of the proposed disposition and shall have furnished the
Company with a statement of the circumstances surrounding the proposed
disposition, and, if reasonably requested by the Company, the Investor shall
have furnished the Company with an opinion of counsel, reasonably satisfactory
to the Company, that such disposition will not require registration of such
Shares under the Securities Act. The Investor shall comply with the requirements
of Section 7 in connection with any proposed disposition. In addition, the
Investor shall not engage in any hedging or other transaction which is designed
to or could reasonably be expected to lead to or result in a disposition of the
Shares by the Investor or any other person or entity. Such prohibited hedging or
other transactions would include without limitation effecting any short sale or
having in effect any short position (whether or not such sale or position is
against the box and regardless of when such position was entered into) or any
purchase, sale or grant of any right (including without limitation any put or
call option) with respect to the Shares or with respect to any security (other
than a broad-based market basket or index) that includes, relates to or derives
any significant part of its value from the Common Stock of the Company, but such
security shall not include the capital stock or debt of the Investor, its parent
companies or their respective subsidiaries.

      d) The certificates evidencing the Shares will bear the following legends:

                                       11


            (i) "THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES
ACT OF 1933. THEY MAY NOT BE SOLD, OFFERED FOR SALE, PLEDGED OR HYPOTHECATED IN
THE ABSENCE OF A REGISTRATION STATEMENT IN EFFECT WITH RESPECT TO THE SECURITIES
UNDER SUCH ACT OR AN OPINION OF COUNSEL REASONABLY SATISFACTORY TO THE COMPANY
THAT SUCH REGISTRATION IS NOT REQUIRED OR UNLESS SOLD PURSUANT TO RULE 144
PROMULGATED UNDER SUCH ACT."

            (ii) Any legend required by the laws of the State of Delaware or
Connecticut.

            The legend referred to in clause (a) above shall be removed by the
Company from any certificate at such time as the holder of the Shares
represented by the certificate delivers an opinion of counsel reasonably
satisfactory to the Company to the effect that such legend is not required in
order to establish compliance with any provisions of the Securities Act, or at
such time as the holder of such Shares satisfies the requirements of Rule 144(k)
under the Securities Act; provided, that Rule 144(k) as then in effect does not
differ substantially from Rule 144(k) as in effect as of the date of this
Agreement; and provided further, that the Company has received from the holder a
written representation that such holder is not an affiliate of the Company and
has not been an affiliate during the preceding three (3) months, such holder has
beneficially owned the Shares represented by the certificate for a period of at
least two (2) years, and such holder otherwise satisfies the requirements of
Rule 144(k) as then in effect with respect to such Shares.

      e) The Investor further represents and warrants to the Company that (i)
the Investor has full right, power, authority and capacity to enter into this
Agreement and the Amendment to Joint Development Agreement and to consummate the
transactions contemplated hereby and thereby and has taken all necessary action
to authorize the execution, delivery and performance of this Agreement and the
Amendment to Joint Development Agreement, and (ii) upon the execution and
delivery of this Agreement and the Amendment to Joint Development Agreement,
each of this Agreement and the Amendment to Joint Development Agreement shall
constitute a valid and binding obligation of the Investor enforceable in
accordance with its terms, except 

                                       12



as enforceability may be limited by applicable bankruptcy, insolvency,
reorganization, moratorium or similar laws affecting creditors' and contracting
parties' rights generally and except as enforceability may be subject to general
principles of equity (regardless of whether such enforceability is considered in
a proceeding in equity or at law).

      f) The Investor understands that nothing in this Agreement or any other
materials presented to the Investor in connection with the purchase and sale of
the Shares constitutes legal, tax or investment advice. The Investor has
consulted such legal, tax and investment advisors as it, in its sole discretion,
has deemed necessary or appropriate in connection of Shares.

      6. Survival of Representations, Warranties and Agreements. Notwithstanding
any investigation made by any party to this Agreement, all covenants,
agreements, representations and warranties made by the Company and the Investor
herein shall survive the execution of this Agreement, the delivery to the
Investor of the Shares and the payment therefor.

      7. Finder's Fee. Each party represents that it neither is nor will be
obligated for any finder's fee or commission in connection with this
transaction, and agrees to indemnify and hold harmless the other from any
liability for any commission or compensation in the nature of a finder's fee
(and the costs and expenses of defending against such liability or asserted
liability) for which it or any of its officers, employees or representatives is
responsible.

      8. Notices. All notices, requests, consents and other communications
hereunder shall be in writing, shall be mailed by first-class registered or
certified airmail, or nationally recognized overnight express courier, postage
prepaid, and shall be deemed given when so mailed and shall be delivered as
addressed as follows:

      a)    if to the Company, to:

            Alexion Pharmaceuticals, Inc.
            25 Science Park, Suite 360
            New Haven, Connecticut
            Attn: David W. Keiser
            Phone:   203-776-1790
            Telecopy: 203-776-2089

                                       13



      b)    with a copy mailed to:

            Golenbock, Eiseman, Assor & Bell
            437 Madison Avenue
            New York, NY 10022-7302
            Attn: Lawrence M. Bell, Esq.
            Phone: 212-907-7300
            Telecopy: 212-754-0330

      c)    if to the Investor, at its address on the signature page hereto, to
            the attention of Thomas R. Bremer, Senior Vice President and General
            Counsel, or at such other address or addresses as may have been
            furnished to the Company in writing.

      9. Changes. This Agreement may not be modified or amended except pursuant
to an instrument in writing signed by the Company and the Investor.

      10. Headings. The headings of the various sections of this Agreement have
been inserted for convenience of reference only and shall not be deemed to be
part of this Agreement.

      11. Severability. In case any provision contained in this Agreement should
be invalid, illegal or unenforceable in any respect, the validity, legality and
enforceability of the remaining provisions contained herein shall not in any way
be affected or impaired thereby.

      12. Governing Law. This Agreement shall be governed by and construed in
accordance with the laws of the State of Delaware and the federal law of the
United States of America.

      13. Choice of Forum; Venue; Service of Process. Any claim, suit, action,
or proceeding among any or all of the parties hereto relating to this Agreement,
to any document, instrument, or agreement delivered pursuant hereto, referred to
herein, or contemplated hereby, or in any other manner arising out of or
relating to the transactions contemplated by or referenced in this Agreement,
shall be commenced and maintained exclusively in the United States District
Court for the District of Connecticut, or, if such Court lacks jurisdiction over
the subject matter, in a state court of competent subject-matter jurisdiction
sitting in the State of Connecticut. The parties hereby submit themselves

                                       14




unconditionally and irrevocably to the personal jurisdiction of such courts. The
parties further agree that venue shall be exclusively in Connecticut. The
parties irrevocably waive any objection to such personal jurisdiction or venue
including, Connecticut but not limited to, the objection that any suit, action,
or proceeding brought in the State of Connecticut has been brought in an
inconvenient forum. The parties irrevocably agree that process issuing from such
courts may be served on them, either personally or by certified mail, return
receipt requested, at the addresses given in Section 8 hereof; and further
irrevocably waive any objection to service of process made in such manner and at
such addresses, including without limitation any objection that service in such
manner and at such addresses is not authorized by the local or procedural laws
of the State of Connecticut.

      14. Counterparts. This Agreement may be executed in two or more
counterparts, each of which shall constitute an original, but all of which, when
taken together, shall constitute but one instrument, and shall become effective
when one or more counterparts have been signed by each party hereto and
delivered to the other parties.

                                       15



                                                                      Exhibit 99

IMMEDIATE RELEASE
- -----------------


   Contact:    Leonard Bell, M.D.                     Rhonda Chiger (Investor)
               President and CEO                      Susan Farley (Media)
               Alexion Pharmaceuticals                Dewe Rogerson Inc.
               203/776-1790                           212/688-6840

                ALEXION RECEIVES $10 MILLION IN PRIVATE PLACEMENT

New Haven, CT, October 1, 1997 --- Alexion Pharmaceuticals, Inc. (Nasdaq: ALXN)
and United States Surgical Corporation (NYSE: USS) have modified their July 1995
joint development agreement in which Alexion granted to U.S. Surgical rights to
certain technologies for commercialization of xenograft tissues for
transplantation. As part of the modification, U.S. Surgical has made an
additional $6.5 million payment to Alexion for equity, exclusive licensing
rights, and certain manufacturing assets.

"We are very excited with the substantial progress that Alexion has made over
the past two years in the development of transgenic pig organs that potentially
can eliminate the waiting lists of tens of thousands of patients who desperately
need organ transplants," said Leon C. Hirsch, chairman of U.S. Surgical. "In
view of this we have increased our commitment to Alexion and our joint research
and development program."

As part of the agreement, Alexion has exclusively licensed an additional patent
application to U.S. Surgical that involves a novel and more efficient method for
the creation of transgenic livestock. The technology was developed in part with
funding from an Advanced Technology Program grant from the National Institute of
Standards and Technology. Alexion has also transferred certain xenograft
manufacturing assets to U.S. Surgical.

"We are gratified that U.S. Surgical has recognized the additional value that
Alexion has brought to our joint development program," said Dr. Leonard Bell,
president and chief executive officer of Alexion. "More importantly, we are very
encouraged by the progress of our collaboration with U.S. Surgical and we expect
continued advances in the months ahead."

Under the modified agreement, U.S. Surgical has made an additional $3 million
equity investment in Alexion through the purchase of 166,945 shares of Alexion
Common Stock at a price of $17.97 per share, which represents a 25% premium over
the market price on the day prior to the date of closing. Additionally, U.S.
Surgical paid to Alexion $3.5 million to acquire technology and xenograft
manufacturing assets. Further, as part of the amended agreement, the parties
have agreed that the preclinical milestone payments in the original agreement
are considered to have been satisfied.





Xenotransplantation refers to the transplantation of non-human organs and
tissues into patients. Genetic modification of porcine cells, tissues, and
organs may allow survival of such foreign cells, tissues and organs after
transplantation into patients.

Alexion Pharmaceuticals, Inc. was founded in 1992 and is engaged in the
development of selective immunotherapeutic drugs that generally are designed to
inhibit the disease-causing segments of the immune system while preserving the
disease preventing aspects of the immune system. The Company is developing three
technology platforms: C5 Complement Inhibitors and Apogen T-Cell Therapeutics
which together target severe cardiovascular and autoimmune disorders; and
xenografts for organ transplants.

United States Surgical Corporation is a diversified surgical products company
specializing in minimally invasive technologies that improve patient care and
lower health care costs.

This news release contains forward looking statements. Such statements are
subject to certain factors which may cause Alexion's plans to differ or results
to vary from those expected including unexpected preclinical or clinical
results, the need for additional research and testing, delays in manufacturing,
access to capital and funding, delays in development of commercial relationships
and a variety of risks set forth from time to time in Alexion's filings with the
Securities and Exchange Commission, including but not limited to Alexion's
Annual Report on Form 10-K for the year ended July 31, 1996 and those risks as
discussed in Alexion's Registration Statement (Registration No. 333-29617).
Alexion undertakes no obligation to publicly release the results of any of these
forward looking statements which may be made to reflect events or circumstances
after the date hereof or to reflect the occurrence of unanticipated events. The
shares of Common Stock sold to U.S. Surgical have not been registered under the
Securities Act of 1933, as amended, and may not be offered and sold in the
United States absent registration under such Act or an applicable exemption from
registration. This press release shall not constitute an offer to sell or the
solicitation of an offer to buy the capital stock of the Company nor shall there
be any sale of these securities in any state in which such offer, solicitation
or sale would be unlawful prior to registration of qualification under the
securities laws of any such state.