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                                                                     EXHIBIT 4.1


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                          SECURITIES PURCHASE AGREEMENT



                                 3,333 SHARES OF
                      SERIES B CONVERTIBLE PREFERRED STOCK,
                          SERIES B WARRANTS TO PURCHASE
                    3,333,000 SHARES OF CLASS A COMMON STOCK.
           AMENDMENT AND RESTATEMENT OF SERIES A WARRANTS TO PURCHASE
                    6,000,000 SHARES OF CLASS A COMMON STOCK
                                       AND
                           REVENUE PARTICIPATION NOTES
                                       OF


                       AMERICAN BIOGENETIC SCIENCES, INC.


                              AS OF AUGUST 23, 2001



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                                TABLE OF CONTENTS

                                                                            PAGE

ARTICLE I - ISSUANCE OF SECURITIES..........................................  2

   1.1   AUTHORIZATION OF SECURITIES........................................  2
   1.2   PURCHASE AND SALE SECURITIES.......................................  2

ARTICLE II - CLOSING........................................................  2

   2.1   CLOSING............................................................  2
   2.2   LEGEND.............................................................  3

ARTICLE III - REPRESENTATIONS AND WARRANTIES OF THE COMPANY.................  3

   3.1   ORGANIZATION AND STANDING OF THE COMPANY...........................  3
   3.2   CAPITALIZATION.....................................................  3
   3.3   VALIDITY AGREEMENT.................................................  4
   3.4   GOVERNMENTAL CONSENT, ETC..........................................  5
   3.5   VALID ISSUANCE OF SECURITIES AND FIRST PRIORITY LIEN...............  5
   3.6   FINANCIAL STATEMENTS...............................................  5
   3.7   ACCURACY AND COMPLETENESS OF INFORMATION...........................  6
   3.8   ADVERSE CHANGES....................................................  6
   3.9   NO VIOLATION.......................................................  6
   3.10  ALL NECESSARY PERMITS..............................................  6
   3.11  TITLE TO PROPERTIES................................................  6
   3.12  SECURITIES LAWS....................................................  7
   3.13  ACCURACY OF RECITALS...............................................  7

ARTICLE IV - REPRESENTATIONS AND WARRANTIES OF THE INVESTORS................  7

   4.1   AUTHORITY OF INVESTORS, VALIDITY OF THIS AGREEMENT.................  7
   4.2   INVESTMENT REPRESENTATIONS.........................................  7

ARTICLE V - CONDITIONS TO INVESTORS' OBLIGATIONS............................  8

   5.1   CONDITIONS TO CLOSING ON CLOSING DATE..............................  8

ARTICLE VI - CONDITIONS TO THE COMPANY'S OBLIGATIONS.......................  10

   6.1   CONDITIONS TO CLOSING.............................................  10

ARTICLE VII - COVENANTS OF THE COMPANY.....................................  11

   7.1   FURNISHING OF INFORMATION.........................................  11
   7.2   INFORMATION WITH RESPECT TO THE SECURITIES........................  11
   7.3   LICENSE AGREEMENT.................................................  11
   7.4   INVESTOR'S RIGHTS.................................................  11
   7.5   EXCHANGE OR MARKET LISTINGS.......................................  12

ARTICLE VIII - PRE-EMPTIVE RIGHTS ON COMPANY ISSUANCES.....................  12

   8.1   PARTICIPATION IN FUTURE OFFERINGS.................................  12
   8.2   NOTICE............................................................  12
   8.3   ACCEPTANCE........................................................  12
   8.4   PERCENTAGE INTEREST...............................................  12
   8.5   NO ACCUMULATION...................................................  13

ARTICLE IX - SURVIVAL AND INDEMNIFICATION..................................  13


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   9.1   SURVIVAL..........................................................  13
   9.2   INDEMNIFICATION...................................................  13

ARTICLE X - MISCELLANEOUS..................................................  14

   10.1  NOTICES...........................................................  14
   10.2  ENTIRE AGREEMENT..................................................  15
   10.3  AMENDMENTS........................................................  15
   10.4  ASSIGNMENT........................................................  16
   10.5  BENEFIT...........................................................  16
   10.6  GOVERNING LAW.....................................................  16
   10.7  SEVERABILITY......................................................  16
   10.8  HEADINGS AND CAPTIONS.............................................  16
   10.9  NO WAIVER OF RIGHTS, POWERS AND REMEDIES..........................  17
   10.10 EXPENSES..........................................................  17
   10.11 BROKERS...........................................................  17
   10.12 CONFIDENTIALITY...................................................  17
   10.13 COUNTERPARTS......................................................  17
   10.14 FURTHER ASSURANCES................................................  18

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                          SECURITIES PURCHASE AGREEMENT

         THIS SECURITIES PURCHASE AGREEMENT (this "Agreement"), is made as of
this 23rd day of August, 2001, by and among AMERICAN BIOGENETIC SCIENCES, INC.,
a Delaware corporation (the "Company"), the investors listed on EXHIBIT A hereto
(collectively, the "Investors"), and certain holders of its previously issued
Series A Convertible Preferred Stock and related Warrants listed on Exhibit A
(the "Series A Holders").

                              W I T N E S S E T H:

         WHEREAS, Company has previously issued to the Series A Holders, 6,000
shares of its Series A Convertible Preferred Stock ("Series A Preferred Stock")
and in conjunction therewith Warrants (each, a "Series A Warrant" and
collectively, the "Series A Warrants") to purchase up to 6,000,000 shares (the
"Series A Warrant Shares") of the Company's Class A Common Stock, par value
$.001 per share (the "Common Stock"); and

         WHEREAS, the Company intends to amend its Restated Certificate of
Incorporation to (i) change the terms of the presently outstanding Series A
Preferred Stock and (ii) designate, out of its authorized but previously
undesignated Preferred Stock, $.001 per share (the "Preferred Stock"), 3,333
shares as the Series B Convertible Preferred Stock (the "Series B Preferred
Stock"), so that the Series A Preferred Stock and the Series B Preferred Stock
shall have the designations, powers, preferences, and other terms set forth on
EXHIBIT B hereto; and

         WHEREAS, the Company and the Series A Holders have agreed to amend the
terms of the Series A Warrants to be substantially in the form of EXHIBIT C
hereto; and

         WHEREAS, the Investors wish to purchase all 3,333 shares of the Series
B Convertible Preferred Stock ( the "Series B Preferred Shares") and the
Company's Series B common stock purchase warrants substantially in the form of
EXHIBIT D hereto (each, a "Series B Warrant" and collectively, the "Series B
Warrants"), entitling the holders to purchase 3,333,000 shares of the Common
Stock (the "Series B Warrant Shares"); and

         WHEREAS, the Company has further agreed to issue to the Investors and
the Series A Holders certain Revenue Participation Notes substantially in the
form of EXHIBIT E hereto, under which a portion of any royalty payments received
by the Company under a certain Exclusive License Agreement with Abbott
Laboratories, an Illinois corporation ("Abbott"), dated January 27, 2000 (the
"Abbott License Agreement") will be paid to the Investors pursuant to the terms
thereof; and

         WHEREAS, the Company has agreed to grant the holders of the Revenue
Participation Notes a first priority security interest in 25% of the royalties
payments received by the Company under the Abbott License Agreement under a
Security Agreement substantially in the form of EXHIBIT F hereto (the "Security
Agreement"); and

         WHEREAS, the Company, the Series A Holders and the Investors have
agreed to provide for the redemption of the Series A Preferred Shares, Series B
Preferred Shares, Amended Series

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A Warrants (as defined in Section 1.1) and Series B Warrants pursuant to the
terms of a Call Option Agreement substantially in the form of EXHIBIT H hereto
(the "Call Option Agreement"); and

         WHEREAS, the Company and the Investors desire to set forth certain
matters to which they have agreed relating to the foregoing;

         NOW THEREFORE, in consideration of the premises and the mutual
covenants contained in this Agreement and other good and valuable consideration,
the parties agree as follows:

ARTICLE I.        ISSUANCE OF SECURITIES

1.1      AUTHORIZATION OF SECURITIES.

         Subject to the terms and conditions of this Agreement, the Company has
authorized, or prior to the Closing (as hereinafter defined) will have
authorized, the issuance of each of (i) the Series B Preferred Shares, (ii) the
Common Stock issuable upon conversion of Series B Preferred Shares, (iii) the
Series B Warrants, (iv) the Series B Warrant Shares, and (v) the Revenue
Participation Notes and has further authorized the amendment and restatement of
the Series A Warrants ("Amended Series A Warrants").

1.2      PURCHASE AND SALE OF SECURITIES.

Subject to the terms and conditions of this Agreement and in reliance upon the
representations and warranties of the Company contained herein, for an aggregate
purchase price of two million forty-one thousand six hundred sixty-two dollars
and fifty cents ($2,041,662.50) ("Purchase Price"), the Investors agree to
purchase from the Company and the Company agrees to sell to the Investors on the
Closing Date (as hereinafter defined): (i) the number of Series B Preferred
Shares set forth opposite each Investor's name on EXHIBIT A attached hereto,
aggregating 3,333 Series B Preferred Shares; (ii) the number of Series B
Warrants set forth opposite each Investor's name on EXHIBIT A attached hereto,
aggregating Warrants to purchase 3,333,000 Series B Warrant Shares; and (iii)
the Revenue Participation Notes in the maximum principal amounts set forth
opposite each Investor's name on EXHIBIT A attached hereto, aggregating in
principal amount up to $25,000,000, subject to adjustment, and to the amendment
and restatement of the Series A Warrants. Notwithstanding the foregoing, the
Investors, by written notice to the Company may reallocate the portion of the
securities to be purchased by any of them, provided that the total amount does
not change.

ARTICLE II.       CLOSING

2.1      CLOSING.

         Subject to the satisfaction of the conditions set forth in Articles VI
and VII hereof, the closing (the "Closing") shall take place at a place and time
(the "Closing Date") mutually agreed by the Company and the Investors, but in
any event no later than five business days after the date hereof. At the
Closing, in consideration of payment of the Purchase Price and other good and
valuable consideration: (i) the Company shall deliver to the Investors one or
more stock

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certificates registered in their names for an aggregate of 3,333 Series B
Preferred Shares; (ii) the Company shall deliver to the Investors one or more
Series B Warrants registered in their names to purchase an aggregate of
3,333,000 Series B Warrant Shares; (iii) the Series A Holders shall receive new
warrant certificates reflecting the amended terms of the Amended Series A
Warrants in exchange for the surrender of their old warrant certificates; and
(iv) the Company shall deliver to the Investors, one or more the Revenue
Participation Notes pursuant to the Revenue Participation Agreement.

2.2      LEGEND.

         The certificates representing the securities being sold and the Revenue
Participation Note shall be subject to a legend restricting transfer under the
Securities Act of 1933, as amended (the "Securities Act"), such legend to be
substantially as follows:

                "THE SECURITIES EVIDENCED HEREBY HAVE NOT BEEN REGISTERED UNDER
                THE SECURITIES ACT OF 1933. THESE SECURITIES MAY NOT BE SOLD OR
                OTHERWISE TRANSFERRED BY ANY PERSON UNLESS (1) EITHER (A) A
                REGISTRATION STATEMENT WITH RESPECT TO SUCH SECURITIES SHALL BE
                EFFECTIVE UNDER THE SECURITIES ACT OF 1933 ("ACT"), OR (B) THE
                COMPANY SHALL HAVE REASONABLY REQUESTED AND RECEIVED AN OPINION
                OF COUNSEL SATISFACTORY TO IT THAT AN EXEMPTION FROM
                REGISTRATION UNDER SUCH ACT IS THEN AVAILABLE, AND (2) THERE
                SHALL HAVE BEEN COMPLIANCE WITH ALL APPLICABLE STATE SECURITIES
                LAWS."

ARTICLE III.      REPRESENTATIONS AND WARRANTIES OF THE COMPANY

         The Company hereby represents and warrants to the Investors and the
Series A Holders that, as of the date of this Agreement, the following are true
and correct:

3.1      ORGANIZATION AND STANDING OF THE COMPANY.

         The Company is a corporation duly organized, validly existing and in
good standing under the laws of the State of Delaware. The Company has full
corporate power and authority to enter into, deliver, and perform its
obligations and undertakings under this Agreement. The Company is duly
authorized to conduct its business and is in good standing under the laws of
each jurisdiction where such qualification is required, except where the lack of
such qualification would not have a material adverse effect on the business,
financial condition, operations, results of operations, or future prospects of
the Company. The Company has full corporate power and authority to carry on the
business in which it is engaged and to own and use the properties owned and as
used by it.

3.2      CAPITALIZATION.

         The Company's entire authorized capital stock consists of: (i)
150,000,000 shares of Class A Common Stock, par value $.001 per share, of which
41,413,909 shares are validly issued

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and outstanding; (ii) 3,000,000 shares of Class B Common Stock, par value $.001
per share (the "Class B Common Stock"), all of which are validly issued and
outstanding; and (iii) 10,000,000 shares of the Preferred Stock par value $.001
per share, of which 7,000 have been designated as Series A Preferred Stock and
are validly issued and outstanding. On or before the Closing, the Company will
file a Certificate of Amendment to its Restated Certificate of Incorporation to
(i) amend the preferences, voting powers, qualifications and special or relative
rights or privileges of the existing Series A Preferred Stock, and (ii)
designate 3,333 shares of the Preferred Stock as Series B Convertible Preferred
Stock and establish the preferences, voting powers, qualifications and special
or relative rights or privileges of such Series B Preferred Stock, both as set
forth in EXHIBIT B (the "Charter Amendment"). The issuance of all presently
issued and outstanding securities was duly authorized, and all such securities
are fully paid and non-assessable. All such issued and outstanding securities
have the preferences, voting powers, qualifications and special or relative
rights or privileges set forth in the Company's Restated Certificate of
Incorporation, as amended as in effect on the date hereof or in the Series A
Warrants, and as of the Closing Date the Series A Preferred Stock and Series B
Preferred Stock will have the preferences, voting powers, qualifications and
special or relative rights or privileges set forth in EXHIBIT B and the Amended
Series A Warrants and Series B Warrants will have the rights set forth in
EXHIBIT C and EXHIBIT D hereto. Other than as indicated on SCHEDULE 3.2 hereto
or in the SEC Reports (as hereinafter defined), the Company does not have
outstanding any option, warrant, purchase right, subscription right, stock
appreciation right, phantom stock right, profit participation right, agreement
or other commitment to issue or to acquire any shares of its capital stock, or
any securities or obligations convertible into or exchangeable for its capital
stock, and the Company has not given any person any right to acquire from the
Company or sell to the Company any shares of its capital stock. There are no
voting trusts, proxies, or other agreements or understandings with respect to
the voting of the capital stock of the Company.

3.3      VALIDITY OF AGREEMENT.

         Subject to approval by the holders of Series A Preferred Stock and
filing of the Charter Amendment; (a) the execution and delivery by the Company
of this Agreement and the performance by the Company of its obligations under
this Agreement, the amendment of the Series A Warrants, and the issuance, sale
and delivery of the Series B Preferred Shares, the Common Stock issuable upon
conversion of the Series B Preferred Shares, the Series B Warrants, and the
Series B Warrant Shares, the Revenue Participation Notes and the Security
Agreement have been duly authorized and approved by all necessary corporate
action; (b) this Agreement has been duly executed and delivered by the Company
and constitutes a valid and binding obligation of the Company, enforceable in
accordance with its terms; and (c) the execution and delivery by the Company of
this Agreement and the performance by the Company of its obligations under this
Agreement, the amendment of the terms of the Series A Warrants, and the
issuance, sale and delivery of the Series B Preferred Shares, the Common Stock
issuable upon conversion of the Series B Preferred Shares, the Series B
Warrants, the Series B Warrant Shares, the Revenue Participation Notes and the
Security Agreement will not (i) conflict with, or result in any breach of any of
the terms of, or constitute a default under, the Restated Certificate of
Incorporation when the same will have been amended by filing of the Charter
Amendment, or By-laws of the Company, (ii) conflict with, result in a breach of
or violation or imposition of any lien, charge or encumbrance upon any property
or assets of the Company or any of its subsidiaries pursuant to, constitute a
default under, result in the acceleration of, create in any

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party the right to accelerate, terminate, modify, or cancel, or require any
notice under, any agreement, instrument, covenant or other restriction or
arrangement to which the Company is a party or by which it or any of its
properties or assets is bound or any statute law, rule, regulation, judgment,
order or decree applicable to the Company or any of its subsidiaries of any
court, regulatory body, administrative agency, governmental body, arbitrator or
other authority having jurisdiction over the Company or any of its subsidiaries
or any of its or their properties.

3.4      GOVERNMENTAL CONSENT, ETC.

         Except for the filing of the Charter Amendment and such other filings,
consents, permits, approvals and authorizations which will be obtained by the
Company prior to the Closing and which are set forth in SCHEDULE 3.4, no
consent, approval, authorization or other order of, action by, filing with, or
notification to any governmental authority is required under existing law or
regulation in connection with the execution, delivery and performance of the
Agreement, the amendment of the Series A Warrants or the offer, issuance, sale
or delivery of the Series B Preferred Shares, the Common Stock issuable upon
conversion of the Series B Preferred Shares, the Series B Warrants, and the
Series B Warrant Shares pursuant to the Agreement or the consummation of any
other transactions contemplated thereby.

3.5      VALID ISSUANCE OF SECURITIES AND FIRST PRIORITY LIEN.

         When issued and delivered against payment therefor in accordance with
the terms and conditions of this Agreement and the Charter Amendment, the
Amended Series A Warrants, the Series A Warrant Shares, the Series B Preferred
Shares, the Common Stock issuable upon conversion of the Series B Preferred
Shares, the Series B Warrants, and the Series B Warrant Shares shall be (i) duly
authorized and validly issued, fully paid and non-assessable and (ii) not
subject to any preemptive rights, liens, claims or encumbrances, or other
restrictions on transfer or other agreements or understandings with respect to
the voting of the Common Stock or the Series B Warrant Shares, except as set
forth in this Agreement or the Charter Amendment. The Revenue Participation
Notes have been duly authorized and, when issued and delivered pursuant to this
Agreement, will have been duly executed, issued and delivered and will
constitute valid and legally binding obligations of the Company enforceable
against the Company in accordance with their terms. At the Closing, the
Investors shall have received a first priority security interest in 25% of the
royalty payments received by the Company under the Abbott License Agreement.

3.6      FINANCIAL STATEMENTS.

         The audited financial statements of the Company contained in the
Company's Annual Report on Form 10-K for the year ended December 31, 2000,
including the notes relating thereto, and the unaudited financial statements of
the Company contained in the Company's Quarterly Reports on Form 10-Q for the
quarters ended March 31, 2001 and June 30, 2001, including the notes thereto,
disclose all material liabilities of the Company as of such dates, except as set
forth on SCHEDULE 3.6 hereto. Such financial statements, including the notes
relating thereto, have been prepared in accordance with generally accepted
accounting principles consistently applied throughout the periods involved. Said
financial statements and related notes fairly present the financial position and
the results of operations and cash flow of Company as of the respective dates
thereof and for the periods indicated.

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3.7      ACCURACY AND COMPLETENESS OF INFORMATION.

         The Common Stock is registered pursuant to Section 12(g) of the
Securities Exchange Act of 1934, as amended (the "Exchange Act"). Copies of all
reports filed by the Company with the United States Securities and Exchange
Commission (the "Commission") pursuant to the Exchange Act during the period
from December 31, 1999 to the date of this Agreement (the "Furnished SEC
Reports") have been furnished to the Investors. Since January 1, 1998, the
Company has filed each statement, annual, quarterly, and other report,
registration statement and definitive proxy statement required to be filed
(other than preliminary material) by the Company with the Commission (the "SEC
Reports"). As of their respective filing dates, the SEC Reports complied in all
material respects with the requirements of the Securities Act or the Exchange
Act, as the case may be, and none of the SEC Reports contained any untrue
statement of a material fact or omitted to state a material fact required to be
stated therein or necessary to make the statements made therein, in light of the
circumstances in which they were made, not misleading.

3.8      ADVERSE CHANGES.

         Since June 30, 2001, except as set forth on SCHEDULE 3.8 hereto, there
has not been any Material Adverse Change. For purposes of this Agreement, a
"Material Adverse Change" means a material adverse change in the business,
earnings, financial condition, results of operations, assets, employee
relations, or customer or supplier relations (in each case whether or not
arising in the ordinary course of business) or presently foreseeable prospects
of the Company and its subsidiaries on an aggregate basis.

3.9      NO VIOLATION.

         Neither the execution and delivery by the Company of this Agreement,
nor the consummation of the transactions contemplated hereby, will violate any
constitution, statute, rule, injunction, judgment, order, decree, ruling, charge
or other restriction of any government, governmental agency, or court known to
the Company to which the Company is subject or, after filing of the Charter
Amendment, any provision of its Restated Certificate of Incorporation or
By-Laws.

3.10     ALL NECESSARY PERMITS, ETC.

         The Company and each subsidiary possesses such valid and current
certificates, authorizations or permits issued by the appropriate state, federal
or foreign regulatory agencies or bodies as are necessary to conduct their
respective businesses, and neither the Company nor any subsidiary has received
any notice of proceedings relating to the revocation or modification of, or
non-compliance with, any such certificate, authorization or permit which, singly
or in the aggregate, if the subject of an unfavorable decision, ruling or
finding, would result in a Material Adverse Change.

3.11     TITLE TO PROPERTIES.

         The Company and each of its subsidiaries has good and marketable title
to all the properties and assets reflected as owned by it in the financial
statements referred to in Section


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3.6, in each case free and clear of any security interests, mortgages, liens,
encumbrances, equities, claims and other defects, except (i) as set forth on
SCHEDULE 3.11, or (ii) such as do not materially and adversely affect the value
of such property and do not materially interfere with the use made or proposed
to be made of such property by the Company or such subsidiary. The real
property, improvements, equipment and personal property held under lease by the
Company or any subsidiary are held under valid and enforceable leases, with such
exceptions as are not material and do not materially interfere with the use made
or proposed to be made of such real property, improvements, equipment or
personal property by the Company or such subsidiary.

3.12     SECURITIES LAWS.

         All notices, filings, registrations or qualifications under state
securities or "blue sky" laws which are required in connection with the
amendment of the Series A Warrants and the offer, issue and delivery of the
Series B Preferred Shares, the Common Stock into which such Series B Preferred
Shares are convertible, the Series B Warrants, the Series B Warrant Shares and
the Revenue Participation Note pursuant to this Agreement have been or will be
timely completed by the Company.

3.13     ACCURACY OF RECITALS.  The recitals hereto are true and accurate.

ARTICLE IV.       REPRESENTATIONS AND WARRANTIES OF THE INVESTORS

         Each of the Investors hereby acknowledges, represents, warrants and
agrees as follows:

4.1      AUTHORITY OF INVESTORS, VALIDITY OF THIS AGREEMENT.

         Each of the Investors has all requisite power and authority to enter
into this Agreement and perform its obligations hereunder. The execution,
delivery and performance by each of the Investors of this Agreement, and the
purchase of the Series B Preferred Shares and Series B Warrants pursuant hereto
have been duly authorized and approved by all necessary corporate action. This
Agreement has been duly executed and delivered and constitutes a valid and
binding obligation of each of the Investors, enforceable in accordance with its
terms. The execution, delivery and performance of this Agreement and the
purchase of the Series B Preferred Shares, Series B Warrants and Revenue
Participation Notes will not conflict with, or result in a material breach of
any of the terms of, or constitute a material default under, any its
organizational documents or agreement, instrument, covenant or other restriction
to which any of the Investors is a party or by which it or any of its properties
or assets is bound.

4.2      INVESTMENT REPRESENTATIONS.

         Each of the Investors hereby acknowledges, represents, warrants and
agrees as follows:

         (a) Each of the Investors has had the opportunity to review the
Furnished SEC Reports and the financial statements contained therein. Each of
the Investors acknowledges that the Company has made available to the Investors
documents and information that it has requested relating to the Company and has
provided answers to the Investors' questions


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concerning the Company, the Series B Preferred Shares, Series B Warrants and
Revenue Participation Notes.

         (b) Each of the Investors is an "accredited investor" as defined in
Rule 501(a)(3) of the Securities Act.

         (c) Each of the Investors understands that the offering of the Series B
Preferred Shares, Series B Warrants and Revenue Participation Notes has not been
registered under the Securities Act or the securities laws of any state or other
jurisdiction and that such Series B Preferred Shares, Series B Warrants and
Revenue Participation Notes must be held indefinitely unless an exemption from
registration is available. Each of the Investors understands that the offering
and sale of the Series B Preferred Shares, Series B Warrants and Revenue
Participation Notes is intended to be exempt from registration under the
Securities Act based, in part, upon the representations, warranties and
agreements of the Investors contained in this Section 4.2, and the Company may
rely on such representations, warranties and agreements in connection therewith.
Each of the Investors covenants that it will not transfer the Series B Preferred
Shares, Series B Warrants and Revenue Participation Notes in violation of the
provisions of any applicable Federal or state securities statute.

         (d) Subject to the Investors' registration rights relating to the
Common Stock underlying their Series B Preferred Shares and Series B Warrants
under the Registration Rights Agreement referred to in Section 5.1 hereof, each
of the Investors is acquiring the Series B Preferred Shares, Series B Warrants
and Revenue Participation Notes for investment, and not with a view to the
resale or distribution thereof, and it has no present intention of selling,
negotiating, or otherwise disposing of the Series B Preferred Shares, Series B
Warrants and Revenue Participation Notes. Each of the Investors' financial
condition and investments are such that it is in a financial position to hold
the Series B Preferred Shares, Series B Warrants and Revenue Participation Notes
for an indefinite period of time and to bear the economic risk of, and withstand
a complete loss of, such Series B Preferred Shares, Series B Warrants and
Revenue Participation Notes. In addition, by virtue of its expertise, the advice
available to it, and its previous investment experience, each of the Investors
has sufficient knowledge and experience in financial and business matters,
investments, securities, and private placements and the capability to evaluate
the merits and risks of the transactions contemplated by this Agreement.

ARTICLE V.        CONDITIONS TO INVESTORS' OBLIGATIONS

5.1      CONDITIONS TO CLOSING ON CLOSING DATE.

         The obligation of the Investors to purchase and pay for the Series B
Preferred Shares, the Series B Warrants and the Revenue Participation Note and
the obligation of the Series A Holders to amend their Series A Warrants on the
Closing Date is subject to the following:

         (a) REPRESENTATIONS AND WARRANTIES. The representations and warranties
of the Company made herein shall be true, correct and complete on and as of the
Closing Date with the same force and effect as if they had been made on and as
of the Closing Date.

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         (b) PERFORMANCE. All covenants, agreements and conditions contained in
this Agreement to be performed or complied with by the Company on or prior to
the Closing Date shall have been performed or complied with.

         (c) OPINION OF COMPANY'S COUNSEL. The Investors shall have received an
opinion of Brown,  Rudnick,  Freed & Gesmer,  counsel for the Company, in form
and substance reasonably satisfactory to the Investors.

         (d) CORPORATE PROCEEDINGS, CONSENTS, ETC. All corporate and other
proceedings to be taken and all waivers and consents to be obtained in
connection with the transactions contemplated by this Agreement shall have been
taken or obtained and all documents incident thereto shall be reasonably
satisfactory in form and substance to the Investors and their counsel, each of
whom shall have received all such originals or certified or other copies of such
documents as each may reasonably request.

         (e) CHARTER AMENDMENT. The Charter Amendment to change the terms of the
Series A Preferred Stock and to designate and fix the terms of the Series B
Preferred Stock so that they have the terms set forth on EXHIBIT B hereto shall
have been filed with the Secretary of State of the State of Delaware.

         (f) NO PROCEEDING. No action, suit, investigation or proceeding shall
be pending or threatened before any court or governmental agency to restrain,
prohibit, collect damages as a result of or otherwise challenge this Agreement
or any transaction contemplated hereby or thereby.

         (g) NO LAW PROHIBITING OR RESTRICTING SUCH SALE. There shall not be in
effect any law, rule or regulation prohibiting or restricting such sale, or
requiring any consent or approval of any person which shall not have been
obtained to issue the Series B Preferred Shares, the Common Stock into which the
Series B Preferred Shares are convertible, the Series B Warrants, Series B
Warrant Shares and Revenue Participation Notes.

         (h) OFFICER'S CERTIFICATE DELIVERED BY COMPANY. The Company shall have
delivered to the Investors a certificate, dated the Closing Date and signed by
the Chief Executive Officer or the President of the Company, to the effect that
each of the conditions to be satisfied by the Company pursuant to this Section
5.1 on or before the Closing Date has been duly satisfied.

         (i) REVENUE PARTICIPATION NOTES. The Company shall have authorized,
issued, executed and delivered the Revenue Participation Notes in the form of
EXHIBIT E.

         (j) SECURITY AGREEMENT. The Company, the Investors, and the Series A
Holders shall have executed and delivered a Security Agreement in the form of
EXHIBIT F hereto.

         (k) REGISTRATION RIGHTS AGREEMENT. The Company, the Investors, and the
Series A Holders shall have executed and delivered a Registration Rights
Agreement in the form of EXHIBIT G hereto.

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         (l) CALL OPTION AGREEMENT. The Company, the Investors, and the Series A
Holders shall have executed and delivered a Call Option Agreement in the form of
EXHIBIT H hereto.

         (m) NO MATERIAL ADVERSE CHANGE. There shall have been no Material
Adverse Change in the Company since the date of signing of this Agreement.

         (n) LEGAL MATTERS. All material matters of a legal nature which pertain
to this Agreement and the transactions contemplated hereby shall have been
reasonably approved by counsel to the Investors.

ARTICLE VI.       CONDITIONS TO THE COMPANY'S OBLIGATIONS

6.1      CONDITIONS TO CLOSING.

         The obligation of the Company to issue the Series B Preferred Shares,
Series B Warrants, to amend the Series A Warrants and issue the Revenue
Participation Notes on the Closing Date is subject to the following:

         (a) REPRESENTATIONS AND WARRANTIES. The representations and warranties
of the Investors made herein shall be true, correct and complete in all respects
on and as of the Closing Date with the same force and effect as if they had been
made on and as of the Closing Date.

         (b) NO PROCEEDING. No action, suit, investigation or proceeding shall
be pending or threatened before any court or governmental agency to restrain,
prohibit, collect damages as a result of or otherwise challenge this Agreement
or any transaction contemplated hereby or thereby.

         (c) NO LAW PROHIBITING OR RESTRICTING SUCH SALE. There shall not be in
effect any law, rule or regulation prohibiting or restricting such sale, or
requiring any consent or approval of any person which shall not have been
obtained to issue the Series B Preferred Shares, Series B Warrants and Revenue
Participation Notes.


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ARTICLE VII.      COVENANTS OF THE COMPANY

         For so long as the Series B Preferred Shares are outstanding, the
Company hereby covenants to such Investors as follows:

7.1      FURNISHING OF INFORMATION.

         The Company covenants to timely file (or obtain extensions in respect
thereof) all reports required to be filed by the Company after the date hereof
pursuant to Section 13(a) or 15(d) of the Exchange Act and to promptly furnish
the Investors with true and complete copies of all such filings. If the Company
is not at the time required to file reports pursuant to such sections, it will
prepare and furnish to the Investors annual and quarterly reports comparable to
those required by Section 13(a) or 15(d) of the Exchange Act in the time period
that such filings would have been required to have been made under the Exchange
Act.

7.2      INFORMATION WITH RESPECT TO THE SECURITIES.

         The Company covenants to provide such information as is reasonably
requested by any of the Investors related to the terms of the Series B Preferred
Shares, the Common Stock issuable upon conversion of Series B Preferred Stock,
Series B Warrants, Series B Warrant Shares, or Revenue Participation Notes.

7.3      LICENSE AGREEMENT.

         The Company covenants that it will not (i) amend the Abbott License
Agreement in any way or manner which would change the amount, timing or other
provisions of such agreement regarding the royalties payable by Abbott
Laboratories to or for the benefit of the Company under the Abbott License
Agreement in any significant way, or (ii) other than as hereafter provided,
agree to any assignment, transfer, conveyance or other disposition by the
Company of any beneficial interest of any nature under the Abbott License
Agreement, in either case without the consent of holders of two-thirds of the
Fractional Percentage held by all Holders of Revenue Participation Notes in any
significant way. However, nothing in the preceding sentence shall prohibit the
Company from (i) granting to any other one or more persons participation
interests in the royalties payable under the Abbott License Agreement, provided
that all such other participation interests cannot in the aggregate entitle such
persons to more than 75% of the royalties payable under the Abbott License
Agreement, or (ii) granting or permitting the creation of a security interest in
any such other participation interest, provided that it is expressly subject to
the prior security interest of the Holders in their Royalty Participation
created by the Security Agreement.

7.4      INVESTOR'S RIGHTS.

         Notwithstanding anything to the contrary in the foregoing, the
Investors shall be entitled to such information, privileges, rights and benefits
accorded to them as holders of the Series B Preferred Shares under applicable
law and under the Company's Restated Articles of Incorporation, as amended, and
By-laws.

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7.5      EXCHANGE OR MARKET LISTINGS

         The Company will use its commercially reasonable efforts to maintain
its listing of the Series A Common Stock on one of the following: any national
exchange in the United States; the Nasdaq National Market; the Nasdaq Smallcap
Market or the OTC Bulletin Board.

ARTICLE VIII.     PRE-EMPTIVE RIGHTS ON COMPANY ISSUANCES

8.1      PARTICIPATION IN FUTURE OFFERINGS.

         Subject to the terms hereof, the Company hereby agrees to offer to each
Investor the opportunity to acquire any equity securities, rights to acquire
equity securities, or securities convertible into equity securities of the
Company which may be offered by the Company from time to time after the date of
this Agreement to unaffiliated investors for capital raising purposes (any such
securities being herein referred to as "New Securities"), all pursuant to the
terms and conditions of this Article.

8.2      NOTICE.

         (a) Each time the Company proposes to offer New Securities, the Company
shall deliver written notice (the "Participation Notice") to each Investor of
the terms and conditions of each transaction pursuant to which the Company
intends to issue New Securities. Such notice shall (i) be delivered to each
Investor at least 48 hours prior to the time at which any such transaction is
scheduled to be consummated, (ii) shall be accompanied by copies of the
documentation for the investment in substantially final form, and (iii) shall
constitute an offer to sell to the Investor the applicable amount of New
Securities calculated pursuant to Section 8.4 upon the same terms and conditions
as the New Securities are being sold to other persons.

         (b) If the Company does not consummate the sale of the New Securities
within forty-five (45) days of delivery of the Participation Notice, or if the
terms and conditions of the proposed investment are materially modified after
delivery of the Participation Notice, the right provided hereunder shall be
deemed to be revived and the Company shall deliver a new Participation Notice to
the Investors, explaining the modifications, and a new 48 hour acceptance period
shall commence upon delivery of the updating notice.

8.3      ACCEPTANCE.

         By written notification delivered to the Company within the 48 hour
acceptance period under Section 8.2, the Investor may elect to accept any such
offer of the New Securities, in whole or in part, at the price and on the terms
specified in the Participation Notice.

8.4      PERCENTAGE INTEREST.

         (a) The amount of New Securities to be offered to each Investor for
purchase pursuant to this Article shall, with respect to each transaction
subject hereto, be calculated by multiplying (i) the aggregate number of New
Securities to be offered, times (ii) that Investor's Percentage Interest.

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         (b) If any Investor fails to exercise its participation rights under
this Article, each other Investor which did elect to participate shall have the
right to purchase up to all the New Securities to which any non-participating
Investor would be entitled, and if more than one participating Investor desires
to purchase such New Securities not purchased by other Investors, those New
Securities shall be allocated among the participating Investors wishing to
purchase them in proportion to their respective Percentage Interests.

(c) For purposes of this Agreement, a person's Percentage Interest shall mean
its percentage ownership of the entire equity capital of the Company, calculated
assuming exercise by that Investor and all other holders of all outstanding
rights, warrants or options for Common Stock, and conversion of all securities
convertible into Common Stock.

8.5      NO ACCUMULATION.

         Each transaction or proposed issuance under this Article is a separate
transaction. The failure of any Investor to exercise in whole or in part any
prior offer shall not affect its rights with respect to any future transaction
subject hereto; and the rights of any Investor under this Article with respect
to any transaction are reduced pro rata to the extent that that Investor
acquires securities of the Company by participating directly in such
transaction.

ARTICLE IX.       SURVIVAL AND INDEMNIFICATION

9.1      SURVIVAL.

         Notwithstanding any examination made by or on behalf of any party
hereto, the knowledge of any party or the acceptance by any party of any
certificate or opinion, each representation, warranty and covenant contained
herein shall survive the Closing for the period that any Series B Preferred
Shares remain outstanding.

9.2      INDEMNIFICATION.

         (a) The Company shall indemnify and hold harmless each Investor, its
shareholders, officers, directors, employees, agents and representatives against
any damage, claim, loss, liability and expense (including reasonable counsel
fees and expenses) which may be suffered or incurred by any of them as a result
of a breach of any representation or warranty or covenant made by the Company in
this Agreement.

         (b) The Investors, jointly and severally, agree to indemnify the
Company and its shareholders, officers, directors, employees, agents and
representatives against any damages, claims, losses, liabilities and expenses
(including reasonable counsel fees and other expenses) which may be suffered or
incurred by it as a result of any breach of any representation, warranty, or
covenant made by the Investors in this Agreement.

         (c) In case any proceeding (including any governmental investigation)
shall be instituted involving any person in respect of which indemnity may be
sought pursuant to this Section, such person (the "indemnified party") shall
promptly notify the person against whom such indemnity may be sought (the
"indemnifying party") in writing of the occurrence of the facts and
circumstances giving rise to such claim. The failure of any person to deliver
the notice

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required by this paragraph shall not in any way affect the indemnifying
party's indemnification obligation hereunder except and only to the extent
that the indemnifying party is actually prejudiced thereby. In case any
such proceeding shall be brought against any indemnified party and it shall
notify the indemnifying party of the commencement thereof, the indemnifying
party shall be entitled to participate therein and, to the extent that it shall
wish, jointly with any other indemnifying party similarly notified, to assume
the defense thereof, with counsel satisfactory to such indemnified party and
shall pay as incurred the fees and expenses of such counsel related to such
proceeding. In any such proceeding, any indemnified party shall have the right
to retain its own counsel or pay its own expenses. Notwithstanding the
foregoing, the indemnifying party shall pay as incurred the fees and expenses of
the counsel retained by the indemnified party in the event (i) the indemnifying
party and the indemnified party shall have mutually agreed to the retention of
such counsel or (ii) the named parties to any such proceedings (including any
impleaded parties) include both the indemnifying party and the indemnified party
and representation of both parties by the same counsel would be inappropriate
due to actual or potential differing interests between them. The indemnifying
party shall not be liable for any settlement of any proceeding effected without
its written consent but if settled with such consent or if there be a final
judgment for the plaintiff, the indemnifying party agrees to indemnify the
indemnified party from and against any loss or liability by reason of such
settlement or judgment and the indemnifying party shall obtain a full release of
the indemnified party.

ARTICLE X.        MISCELLANEOUS

10.1     NOTICES.

         All notices, requests, consents and other communications hereunder
shall be in writing, shall be addressed to the receiving party's address set
forth below or to such other address as a party may designate by notice
hereunder, and shall be either (i) delivered by hand, (ii) made by telecopy or
facsimile transmission, (iii) sent by recognized national overnight courier
service, or (iv) sent by registered mail, return receipt requested, postage
prepaid.

If to the
Investors:                 c/o BVF Partners, L.P.
                           One Sansome Street, 39th Floor
                           San Francisco, CA 94104
                           Attn: Mr.  Mark Lampert
                           Fax: (415) 288-2394

With a copy to:   Pillsbury Winthrop LLP
                           50 Fremont Street, 8th Floor
                           San Francisco, CA  94105
                           Attn:  Jonathan D. Joseph, Esq.
                           Fax: (415) 983-1200

If to Alfred J. Roach:     c/o American Biogenetic Sciences, Inc.
                           1375 Akron Street
                           Copiague, New York 11726
                           Attn: Chief Executive Officer


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                           Fax: (516) 789-1661

With a copy to:            Brown, Rudnick, Freed & Gesmer
                           One Financial Center
                           Boston, Massachusetts 02111
                           Attn: David H. Murphree, Esq.
                           Fax: (617) 856-8201

If to the Company:         American Biogenetic Sciences, Inc.
                           1375 Akron Street
                           Copiague, New York 11726
                           Attn: Chief Executive Officer
                           Fax: (516) 789-1661

With a copy to:            Brown, Rudnick, Freed & Gesmer
                           One Financial Center
                           Boston, Massachusetts 02111
                           Attn: David H. Murphree, Esq.
                           Fax: (617) 856-8201

All notices, requests, consents and other communications hereunder shall be
deemed to have been given either (i) if by hand, at the time of the delivery
thereof to the receiving party at the address of such party set forth above,
(ii) if made by telecopy or facsimile transmission, on the next business day
after the time that receipt thereof has been acknowledged by electronic
confirmation or otherwise, (iii) if sent by overnight courier, on the next
business day following the day such notice is delivered to the courier service,
or (iv) if sent by registered mail, on the fifth business day following the day
such mailing is made.

10.2     ENTIRE AGREEMENT.

         This Agreement, including exhibits, or other documents referred to
herein, embodies the entire agreement and understanding between the parties
hereto with respect to the subject matter hereof and supersedes all prior oral
or written agreements and understandings relating to the subject matter hereof.
No statement, representation, warranty, covenant or agreement of any kind not
expressly set forth in this Agreement shall affect, or be used to interpret,
change or restrict, the express terms and provisions of this Agreement.

10.3     AMENDMENTS.

         On or prior to the Closing Date, the terms and provisions of the
Agreement may be modified, amended or waived, or consent for the departure
therefrom granted, only by written agreement of the Company, the Investors
holding a majority of the Percentage Interest of the Investors, and a majority
in interest of the Series A Holders. After the Closing Date, the terms and
provisions of the Agreement may be modified, amended or waived, or consent for
the departure therefrom granted, only by written agreement of the Company,
Alfred J. Roach, Investors holding a majority of the Percentage Interest of the
Investors, and a majority in interest of the Series A Holders. No such waiver or
consent, in either case, shall be deemed to be or shall

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constitute a waiver or consent with respect to any other terms or
provisions of this Agreement, whether or not similar. Each such waiver or
consent, in either case, shall be effective only in the specific instance and
for the purpose for which it was given, and shall not constitute a continuing
waiver or consent.

10.4     ASSIGNMENT.

         Neither this Agreement nor any or all of the rights and obligations of
a party hereunder shall be assigned, delegated, sold, transferred or otherwise
disposed of by operation of law or otherwise, to any third person without the
prior written consent of the other party, and any attempted assignment,
delegation, sale, transfer, or other disposition, by operation of law or
otherwise, of this Agreement or of any rights or obligations hereunder contrary
to this Section shall be void and without force or effect. Each party shall be
responsible for the compliance by its Affiliates with the terms and conditions
of this Agreement.

10.5     BENEFIT.

         All statements, representations, warranties, covenants and agreements
in this Agreement shall be binding on the parties hereto and shall inure to the
benefit of the respective successors and permitted assigns of each party hereto.
Nothing in this Agreement shall be construed to create any rights or obligations
except among the parties hereto, and no person or entity shall be regarded as a
third-party beneficiary of this Agreement.

10.6     GOVERNING LAW.

         This Agreement and the rights and obligations of the parties hereunder
shall be construed in accordance with and governed by the substantive laws of
the State of New York exclusive of choice of law provisions.

10.7     SEVERABILITY.

         In the event that any court of competent jurisdiction shall determine
that any provision, or any portion thereof, contained in this Agreement shall be
unreasonable or unenforceable in any respect, then such provision shall be
deemed limited to the extent that such court deems it reasonable and
enforceable, and as so limited shall remain in full force and effect. In the
event that such court shall deem any such provision, or portion thereof, wholly
unenforceable, the remaining provisions of this Agreement shall be interpreted
as if such provision were so excluded and shall nevertheless remain in full
force and effect.

10.8     HEADINGS AND CAPTIONS.

         The headings and captions of the various subdivisions of this Agreement
are for convenience of reference only and shall in no way modify, or affect the
meaning or construction of any of the terms or provisions hereof.

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10.9     NO WAIVER OF RIGHTS, POWERS AND REMEDIES.

         No failure or delay by a party hereto in exercising any right, power or
remedy under this Agreement, and no course of dealing between the parties
hereto, shall operate as a waiver of any such right, power or remedy of the
party. No single or partial exercise of any right, power or remedy under this
Agreement by a party hereto, nor any abandonment or discontinuance of steps to
enforce any such right, power or remedy, shall preclude such party from any
other or further exercise thereof or the exercise of any other right, power or
remedy hereunder. The election of any remedy by a party hereto shall not
constitute a waiver of the right of such party to pursue other available
remedies. No notice to or demand on a party not expressly required under this
Agreement shall entitle the party receiving such notice or demand to any other
or further notice or demand in similar or other circumstances or constitute a
waiver of the rights of the party giving such notice or demand to any other or
further action in any circumstances without such notice or demand.

10.10    EXPENSES.

         Except as provided in Section 9.2, each of the parties shall pay its
own fees and expenses (including the fees of any attorneys, accountants,
appraisers or others engaged by such party) in connection with this Agreement
and the transactions contemplated hereby whether or not the transactions
contemplated hereby are consummated; provided, that, the Company shall pay such
fees and expenses (including attorney's fees of Pillsbury Winthrop LLP) of the
Investors in an amount agreed upon, in good faith, by the Company and the
Investors.

10.11    BROKERS.

         Each of the parties hereto represents and warrants to the other that no
broker, finder or financial consultant has acted on its behalf in connection
with this Agreement or the transactions contemplated hereby in such a way as to
create any liability on the other. Each of the parties hereto agrees to
indemnify and save the other harmless from any claim or demand for commission or
other compensation by any other broker, finder, financial consultant or similar
agent claiming to have been employed by or on behalf of such party and to bear
the cost of legal expenses incurred in defending against any such claim.

10.12    CONFIDENTIALITY.

         The Investors acknowledge and agree that any information or data they
have acquired from the Company, which is clearly designated in writing as
confidential and is not otherwise properly in the public domain, was received in
confidence. Each of the Investors agrees not to divulge, communicate or
disclose, except as may be required by law or upon the advice of its counsel or
for the performance of this Agreement, or use to the detriment of the Company or
for the benefit of any other person or persons, or misuse in any way, any
confidential information of the Company.

10.13    COUNTERPARTS.


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         This Agreement may be executed in one or more counterparts, and by
different parties hereto on separate counterparts, each of which shall be deemed
an original, but all of which together shall constitute one and the same
instrument.

10.14    FURTHER ASSURANCES.

         In case at any time after the Closing any further action is necessary
or desirable to carry out the purposes of this Agreement, the Company and the
Investors will take such further action as the other party may reasonably
request, all at the sole cost and expense of the requesting party (unless the
requesting party is entitled to indemnification therefor under Article IX).

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<PAGE>   22




         IN WITNESS WHEREOF, the undersigned have executed this Securities
Purchase Agreement as of this __ day of August, 2001.


                                       AMERICAN BIOGENETIC SCIENCES, INC.


                                       By:
                                          --------------------------------------
                                          Name:    Josef C. Schoell
                                          Title:   President, COO and CFO



                                      SERIES A HOLDERS:

                                      BIOTECHNOLOGY VALUE FUND, L.P.

                                      By: BVF PARTNERS L.P., its General Partner

                                          By: BVF, INC., its General Partner


                                              By : _____________________________
                                                   Mark N. Lampert
                                                   President

                                      BIOTECHNOLOGY VALUE FUND II, L.P.

                                      By: BVF PARTNERS L.P., its General Partner

                                          By: BVF, INC., its General Partner

                                              By:  _____________________________
                                                   Mark N. Lampert
                                                   President

                                      INVESTMENT 10 L.L.C.

                                      By: BVF PARTNERS, L.P., its Investment
                                          Advisor

                                          By: BVF, INC., its General Partner


                                              By:  _____________________________
                                                   Mark N. Lampert
                                                   President

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<PAGE>   23

                                      SERIES B INVESTORS:

                                      BIOTECHNOLOGY VALUE FUND, L.P.

                                      By: BVF PARTNERS L.P., its General Partner

                                          By: BVF, INC., its General Partner


                                              By: ______________________________
                                                  Mark N. Lampert
                                                  President

                                      BIOTECHNOLOGY VALUE FUND II, L.P.

                                      By: BVF PARTNERS L.P., its General Partner

                                          By: BVF, INC., its General Partner


                                              By: ______________________________
                                                  Mark N. Lampert
                                                  President

                                      INVESTMENT 10 L.L.C.

                                      By: BVF PARTNERS, L.P., its Investment
                                          Advisor

                                          By: BVF, INC., its General Partner


                                              By: ______________________________
                                                  Mark N. Lampert
                                                  President

                                      BVF INVESTMENTS, L.L.C.

                                      By: BVF PARTNERS, L.P., its Investment
                                          Advisor

                                          By: BVF, INC., its General Partner


                                              By: ______________________________
                                                  Mark N. Lampert
                                                  President

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<PAGE>   24

                                LIST OF EXHIBITS

--------------------------------------------------------------------------------
EXHIBIT A                  LIST OF INVESTORS AND SERIES A HOLDERS
--------------------------------------------------------------------------------
EXHIBIT B                  TERMS OF PREFERRED STOCK
--------------------------------------------------------------------------------
EXHIBIT C                  FORM OF AMENDED AND RESTATED SERIES A WARRANT
--------------------------------------------------------------------------------
EXHIBIT D                  FORM OF SERIES B WARRANT
--------------------------------------------------------------------------------
EXHIBIT E                  FORM OF REVENUE PARTICIPATION NOTE
--------------------------------------------------------------------------------
EXHIBIT F                  FORM OF SECURITY AGREEMENT
--------------------------------------------------------------------------------
EXHIBIT G                  FORM OF REGISTRATION RIGHTS AGREEMENT
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EXHIBIT H                  FORM OF CALL OPTION AGREEMENT
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                                    EXHIBIT A
                                       TO
                          SECURITIES PURCHASE AGREEMENT


                                   INVESTORS:

--------------------------------------------------------------------------------
                                       NO. OF                        REVENUE
                                     SHARES OF                    PARTICIPATION
                                     SERIES B        NO. OF       NOTE PRINCIPAL
       NAME AND ADDRESS              PREFERRED      WARRANTS           AMOUNT
--------------------------------------------------------------------------------

SERIES B INVESTORS:

BIOTECHNOLOGY VALUE FUND, L.P.         1,167       1,167,000       $8,751,205.40
BIOTECHNOLOGY VALUE FUND II, L.P.        600         600,000      $11,250,401.80
INVESTMENT 10 L.L.C.                     166         166,000       $1,248,258.87
BVF INVESTMENTS, L.L.C.                1,400       1,400,000       $3,750,133.93
Total                                  3,333       3,333,000         $25,000,000


                                SERIES A HOLDERS:

--------------------------------------------------------------------------------
                               NAME AND ADDRESS         NO. OF AMENDED SERIES A
                                                               WARRANTS
--------------------------------------------------------------------------------

SERIES A HOLDERS:

BIOTECHNOLOGY VALUE FUND, L.P.                                   2,100

BIOTECHNOLOGY VALUE FUND II, L.P.                                3,600

INVESTMENT 10 L.L.C.                                               300

Total                                                            6,000

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                                    EXHIBIT B
                                       TO
                          SECURITIES PURCHASE AGREEMENT


                            TERMS OF PREFERRED STOCK



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                                    EXHIBIT C
                                       TO
                          SECURITIES PURCHASE AGREEMENT


                        FORM OF AMENDED SERIES A WARRANT



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                                    EXHIBIT D
                                       TO
                          SECURITIES PURCHASE AGREEMENT


                            FORM OF SERIES B WARRANT



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                                    EXHIBIT E
                                       TO
                          SECURITIES PURCHASE AGREEMENT


                     FORM OF REVENUE PARTICIPATION AGREEMENT


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                                    EXHIBIT F
                                       TO
                          SECURITIES PURCHASE AGREEMENT


                               SECURITY AGREEMENT


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                                    EXHIBIT G
                                       TO
                          SECURITIES PURCHASE AGREEMENT


                          REGISTRATION RIGHTS AGREEMENT




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                                    EXHIBIT H
                                       TO
                          SECURITIES PURCHASE AGREEMENT


                              CALL OPTION AGREEMENT





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