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                                                                         DOC. 3
                                                                   EXHIBIT 10.3


                       DEVELOPMENT AND COMMERCIALIZATION
                               AGREEMENT (NO. 2)
                                           
                                           
                                           
                                    BETWEEN
                                           
                                           
                                           
                                COCENSYS, INC.,
                                           
                                           
                                      AND
                                           
                                           
                           WYETH-AYERST LABORATORIES
                                           

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                               TABLE OF CONTENTS

                                                                           PAGE

1.  DEFINITIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  1
    1.1  "Affiliate(s)". . . . . . . . . . . . . . . . . . . . . . . . . . .  1
    1.2  "Agreement (No. 1)" . . . . . . . . . . . . . . . . . . . . . . . .  1
    1.3  "Back-Up Compound Candidate". . . . . . . . . . . . . . . . . . . .  1
    1.4  "Back-Up Program" . . . . . . . . . . . . . . . . . . . . . . . . .  2
    1.5  "Beginning of [     *     ] . . . . . . . . . . . . . . . . . . . .  2
    1.6  "Beginning of [     *     ] . . . . . . . . . . . . . . . . . . . .  2
    1.7  "CO 2-6749" . . . . . . . . . . . . . . . . . . . . . . . . . . . .  2
    1.8  "CoCensys Patent Rights". . . . . . . . . . . . . . . . . . . . . .  2
    1.9  "Commercially Reasonable Efforts" . . . . . . . . . . . . . . . . .  2
    1.10 "Control" . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  2
    1.11 "Development" . . . . . . . . . . . . . . . . . . . . . . . . . . .  2
    1.12 "Epalon". . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  2
    1.13 "FDA" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  2
    1.14 "Field" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  2
    1.15 "First Commercial Sale" . . . . . . . . . . . . . . . . . . . . . .  3
    1.16 "Fully Burdened Cost" . . . . . . . . . . . . . . . . . . . . . . .  3
    1.17 "Good Clinical Practice". . . . . . . . . . . . . . . . . . . . . .  3
    1.18 "Good Laboratory Practice". . . . . . . . . . . . . . . . . . . . .  3
    1.19 "Good Manufacturing Practice" . . . . . . . . . . . . . . . . . . .  3
    1.20 [     *     ] . . . . . . . . . . . . . . . . . . . . . . . . . . .  3
    1.21 "IND" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
    1.22 "Intellectual Property Rights". . . . . . . . . . . . . . . . . . .  4
    1.23 "Invention" . . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
    1.24 "Know-How". . . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
    1.25 "Licensed Compound" . . . . . . . . . . . . . . . . . . . . . . . .  5
    1.26 "MAA" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
    1.27 "Major Market Countries". . . . . . . . . . . . . . . . . . . . . .  5
    1.28 "NDA" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
    1.29 "Net Sales" . . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
    1.30 [     *     ] . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
    1.31 "Non-Scheduled Product" . . . . . . . . . . . . . . . . . . . . . .  5
    1.32 "Patent Rights" . . . . . . . . . . . . . . . . . . . . . . . . . .  6
    1.33 "Phase I," "Phase II," and "Phase III". . . . . . . . . . . . . . .  6
    1.34 "Product" . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
    1.35 "Regulatory Approval" . . . . . . . . . . . . . . . . . . . . . . .  6
    1.36 "RoW" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
    1.37 "Royalty Term". . . . . . . . . . . . . . . . . . . . . . . . . . .  6
    1.38 "Scheduled Product" . . . . . . . . . . . . . . . . . . . . . . . .  6


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                               TABLE OF CONTENTS
                                   (CONTINUED)

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    1.39 "Third Party(ies)". . . . . . . . . . . . . . . . . . . . . . . . .  7
    1.40 "Trademark" . . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
    1.41 "USA" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
    1.42 "Wyeth-Ayerst Patent Rights". . . . . . . . . . . . . . . . . . . .  7

2.  DEVELOPMENT OF LICENSED COMPOUND . . . . . . . . . . . . . . . . . . . .  7
    2.1  General Obligations . . . . . . . . . . . . . . . . . . . . . . . .  7
    2.2  Records, Reports and Information Exchange . . . . . . . . . . . . .  7
    2.3  Compliance. . . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
    2.4  Funding of the Development. . . . . . . . . . . . . . . . . . . . .  8
    2.5  Regulatory Approvals. . . . . . . . . . . . . . . . . . . . . . . .  8

3.  BACK-UP COMPOUND CANDIDATES. . . . . . . . . . . . . . . . . . . . . . .  8

4.  INDICATIONS; EXCLUSIVITY . . . . . . . . . . . . . . . . . . . . . . . .  8
    4.1  Indications . . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
    4.2  No [     *     ]by CoCensys [     *     ] . . . . . . . . . . . . .  9
    4.3  No [     *     ]. . . . . . . . . . . . . . . . . . . . . . . . . .  9

5.  LICENSE GRANTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  9
    5.1  Licenses to Wyeth-Ayerst. . . . . . . . . . . . . . . . . . . . . .  9
    5.2  Licenses upon Expiration. . . . . . . . . . . . . . . . . . . . . . 10

6.  CONSIDERATION TO COCENSYS. . . . . . . . . . . . . . . . . . . . . . . . 10
    6.1  Payments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
    6.2  Method of Payment of Payments . . . . . . . . . . . . . . . . . . . 11
    6.3  Payments for Back-Up Compound Candidates. . . . . . . . . . . . . . 11
    6.4  Royalties and Profit Sharing. . . . . . . . . . . . . . . . . . . . 11

7.  MARKETING AND ROYALTIES IN THE ROW . . . . . . . . . . . . . . . . . . . 11
    7.1  Marketing by Wyeth-Ayerst . . . . . . . . . . . . . . . . . . . . . 11
    7.2  Commercial and Regulatory Diligence . . . . . . . . . . . . . . . . 11
    7.3  Annual Net Sales Calculation. . . . . . . . . . . . . . . . . . . . 12
    7.4  Non-Scheduled Product Royalty in the RoW. . . . . . . . . . . . . . 12
    7.5  Scheduled Product Royalty.. . . . . . . . . . . . . . . . . . . . . 12
    7.6  Payments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
    7.7  Adjustment to Royalties in RoW. . . . . . . . . . . . . . . . . . . 13


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                               TABLE OF CONTENTS
                                   (CONTINUED)

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8.  ACCOUNTS AND RECORDS . . . . . . . . . . . . . . . . . . . . . . . . . . 14
    8.1  Records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
    8.2  Audits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
    8.3  Foreign Exchange. . . . . . . . . . . . . . . . . . . . . . . . . . 15
    8.4  Sales by Sublicensees . . . . . . . . . . . . . . . . . . . . . . . 15
    8.5  Currency Blockage . . . . . . . . . . . . . . . . . . . . . . . . . 15
    8.6  Withholding . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

9.  TRADEMARKS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

10. MANUFACTURING AND DISTRIBUTION . . . . . . . . . . . . . . . . . . . . . 16
    10.1 Primary Manufacture . . . . . . . . . . . . . . . . . . . . . . . . 16
    10.2 Second Source . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
    10.3 Exchange of Information . . . . . . . . . . . . . . . . . . . . . . 16
    10.4 Compliance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

11. PROSECUTION, MAINTENANCE AND INFRINGEMENT OF INTELLECTUAL PROPERTY
    RIGHTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
    11.1 Patentable Inventions . . . . . . . . . . . . . . . . . . . . . . . 16
    11.2 Prosecution and Maintenance of Patent Rights. . . . . . . . . . . . 17
    11.3 Patent Extensions . . . . . . . . . . . . . . . . . . . . . . . . . 17
    11.4 Cooperation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
    11.5 Infringement of Intellectual Property Rights. . . . . . . . . . . . 18
    11.6 Infringement of Third Party Patent Rights . . . . . . . . . . . . . 19

12. FORCE MAJEURE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

13. TERM AND TERMINATION . . . . . . . . . . . . . . . . . . . . . . . . . . 20
    13.1 General Conditions of Expiration and Termination. . . . . . . . . . 20
    13.2 Term. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
    13.3 Termination for Breach. . . . . . . . . . . . . . . . . . . . . . . 21
    13.4 No Limit on Remedies. . . . . . . . . . . . . . . . . . . . . . . . 22
    13.5 Unilateral Termination by Wyeth-Ayerst. . . . . . . . . . . . . . . 22
    13.6 Automatic Termination of Agreement (No. 1). . . . . . . . . . . . . 22

14. ASSIGNMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
    14.1 Assignment to Affiliates. . . . . . . . . . . . . . . . . . . . . . 22
    14.2 Other Permitted Assignment. . . . . . . . . . . . . . . . . . . . . 22
    14.3 Binding Nature of Assignment. . . . . . . . . . . . . . . . . . . . 22


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                               TABLE OF CONTENTS
                                   (CONTINUED)

                                                                           PAGE


15. INDEMNIFICATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
    15.1 Cross Indemnification . . . . . . . . . . . . . . . . . . . . . . . 23
    15.2 Insurance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

16. WARRANTIES AND REPRESENTATIONS . . . . . . . . . . . . . . . . . . . . . 24
    16.1 General.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

17. CONFIDENTIAL INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . 24
    17.1 Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
    17.2 Exceptions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
    17.3 Permitted Disclosures . . . . . . . . . . . . . . . . . . . . . . . 25
    17.4 Disclosure of Agreement . . . . . . . . . . . . . . . . . . . . . . 25
    17.5 Publicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
    17.6 Publication . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

18. MISCELLANEOUS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
    18.1 No Waiver of Contractual Rights . . . . . . . . . . . . . . . . . . 26
    18.2 Execution and Amendments. . . . . . . . . . . . . . . . . . . . . . 26
    18.3 Severability. . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
    18.4 Relationship between the Parties. . . . . . . . . . . . . . . . . . 26
    18.5 Correspondence and Notices. . . . . . . . . . . . . . . . . . . . . 26
    18.6 Choice of Law . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
    18.7 Counterparts. . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
    18.8 Appointment of Wyeth-Ayerst International, Inc. . . . . . . . . . . 27


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                 DEVELOPMENT AND COMMERCIALIZATION AGREEMENT (NO. 2)


    THIS DEVELOPMENT AND COMMERCIALIZATION AGREEMENT (NO. 2) (the 
"Agreement") is entered into as of the 12th day of May, 1997 (the "Effective 
Date"), by and between CoCensys, Inc., a company incorporated under the laws 
of the State of Delaware, with its principal place of business at 213 
Technology Drive, Irvine, California 92618, USA ("CoCensys"), and American 
Home Products Corporation, acting through its Wyeth-Ayerst Laboratories 
Division, a company incorporated under the laws of the State of Delaware, 
with its principal place of business at 555 Lancaster Avenue, St. Davids, 
Pennsylvania 19087, USA ("Wyeth-Ayerst"). Both CoCensys and Wyeth-Ayerst are 
referred to individually as a "Party" and collectively as the "Parties."

    WHEREAS, CoCensys has discovered, has rights to and is developing that 
certain compound CO 2-6749 (as defined in Article 1.8 below); and

    WHEREAS, Wyeth-Ayerst would like to obtain the worldwide (except in the 
USA) rights to develop and commercialize CO 2-6749 or a back-up compound 
therefor; 

    NOW, THEREFORE, in consideration of the foregoing premises and the mutual 
premises, covenants and conditions contained in this Agreement, the Parties 
agree as follows:

1.  DEFINITIONS.

    For the purposes of this Agreement, the terms hereunder shall have the
    meanings as defined below:

    1.1  "AFFILIATE(S)" shall mean, in the case of either CoCensys or 
         Wyeth-Ayerst, any corporation, joint venture, or other business 
         entity which directly or indirectly controls, is controlled by, or is 
         under common control with that Party. "Control," as used in this 
         Article 1.1, shall mean having the power to direct, or cause the 
         direction of, the management and policies of an entity, whether 
         through ownership of voting securities, by contract or otherwise.

    1.2  "AGREEMENT (NO. 1)" shall mean that Development and Commercialization
         Agreement (No.1) between the Parties relating to development and
         commercialization of CO 2-6749 or a back-up compound therefore in the
         USA, entered into on even date with the Effective Date.

    1.3  "BACK-UP COMPOUND CANDIDATE" shall mean any Epalon meeting the
         criteria set forth in Exhibit A as determined by CoCensys and
         submitted by CoCensys to Wyeth-Ayerst as a potential substitute for CO
         2-6749.  "Back-Up Compound Candidate" shall include any prodrugs, salt
         forms and other biologically active isomers or enantiomers of such
         CoCensys Epalon.


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    1.4  "BACK-UP PROGRAM" shall mean the program for identification of Back-Up
         Compound Candidates as conducted by CoCensys pursuant to Agreement
         (No. 1)

    1.5  "BEGINNING OF [     *     ] shall mean the date upon which the 
         [       *          ] for a Product.

    1.6  "BEGINNING OF [     *     ] shall mean the date upon which the 
         [       *          ] for a Product.

    1.7  "CO 2-6749" shall mean the Epalon [          *          ] and any
         prodrugs, including specifically CO 6-0549, salt forms and other
         biologically active isomers or enantiomers of this Epalon.  A diagram
         of the chemical structure of each of CO 2-6749 and CO 6-0549 is set
         forth on Exhibit B.

    1.8  "COCENSYS PATENT RIGHTS" shall mean all Patent Rights owned or
         Controlled by CoCensys.  A list of the CoCensys Patent Rights existing
         as of the Effective Date is set out in Exhibit C hereto.

    1.9  "COMMERCIALLY REASONABLE EFFORTS" shall mean efforts and resources
         normally used by a party for a compound owned by it or to which it has
         rights, which is of similar market potential at a similar stage in its
         product life, taking into account the competitiveness of the
         marketplace, the proprietary position of the compound, the regulatory
         structure involved, the profitability of the applicable products, and
         other relevant factors.

    1.10 "CONTROL" shall mean licensed with the right to grant sublicenses
         without violating the terms of any Third Party agreement.

    1.11 "DEVELOPMENT" shall mean the pre-clinical development of a Licensed
         Compound and clinical development for use in the Field in the RoW of a
         Product through and including Regulatory Approval.

    1.12 "EPALON" shall mean the class of neuroactive steroid compounds that
         interact with GABAA receptor complexes.

    1.13 "FDA" shall mean the Food and Drug Administration of the USA.

    1.14 "FIELD" shall mean the treatment in humans of [          *          ]
         in the Diagnostic and Statistical Manual of Mental Disorders, Fourth
         Edition ("DSM-IV").  Also, specifically to be included under [         
         *          ] defined by research criteria in DSM-IV.  It is understood
         by the Parties that the above-named disorders may be defined
         differently in future editions of the Diagnostic and 


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         Statistical Manual of Mental Disorders, but that, for purposes of 
         this Agreement, the definition of Field shall always be with 
         reference to those diseases which fall within the definition of the 
         above-named disorders in the edition of DSM-IV which is current as of 
         the Effective Date. Expressly excluded from the Field are 
         [          *          ].

    1.15 "FIRST COMMERCIAL SALE" shall mean the first sale of a Product in a
         given country after the Product has been granted Regulatory Approval
         by the competent authorities in that country.

    1.16 "FULLY BURDENED COST" shall mean the sum of the costs set forth on
         Exhibit D, to the extent allocable to Product.  

    1.17 "GOOD CLINICAL PRACTICE" or "GCP" shall mean the then current
         standards for clinical trials for pharmaceuticals, as set forth in the
         United States Federal Food, Drug and Cosmetics Act and applicable
         regulations promulgated thereunder, as amended from time to time, and
         such standards of good clinical practice as are required by the
         European Union and other organizations and governmental agencies in
         countries in which the Product is intended to be sold, to the extent
         such standards are not in contravention with United States GCP.

    1.18 "GOOD LABORATORY PRACTICE" or "GLP" shall mean the then current
         standards for laboratory activities for pharmaceuticals, as set forth
         in the United States Federal Food, Drug and Cosmetics Act and
         applicable regulations promulgated thereunder, as amended from time to
         time, and such standards of good laboratory practice as are required
         by the European Union and other organizations and governmental
         agencies in countries in which the Product is intended to be sold, to
         the extent such standards are not in contravention with United States
         GLP.

    1.19 "GOOD MANUFACTURING PRACTICE" or "GMP" shall mean the current
         standards for the manufacture of pharmaceuticals, as set forth in the
         United States Federal Food, Drug and Cosmetics Act and applicable
         regulations promulgated hereunder, as amended from time to time, and
         such standards of good manufacturing practice as are required by the
         European Union and other organizations and governmental agencies in
         countries in which the Product is intended to be sold, to the extent
         such standards are not in contravention with United States GMP.

    1.20 [          *          ] shall mean the development milestone 
         [          *          ].

    1.21 "IND" shall mean an Investigational New Drug Application as defined in
         the United States Federal Food, Drug and Cosmetics Act and applicable
         regulations promulgated thereunder, as amended from time to time.  


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    1.22 "INTELLECTUAL PROPERTY RIGHTS" shall mean all Patent Rights,
         trademarks, copyrights, know-how and/or trade secrets which are owned
         or Controlled by one Party hereto (with the right to license) or
         jointly by the Parties, with regard to the development, manufacture,
         importing, use, marketing and/or sale of the Product.

    1.23 "INVENTION" shall mean an invention conceived in the course of the
         performance of and within the scope of this Agreement.

    1.24 "KNOW-HOW" shall mean all know-how, processes, information and data
         including any copyright relating thereto owned or controlled by either
         Party (with the right to have or disclose) as of the Effective Date or
         acquired during the term of this Agreement relating to:

         (a)  the Licensed Compound;

         (b)  any Back-Up Compound;

         (c)  any Product containing (a) or (b);

         (d)  methods of making any of (a), (b) or (c);

         (e)  any component of (c);

         (f)  any intermediate in the making of any of (a), (b), (c), or (e);

         (g)  any method of using any of (a), (b), (c), (e), or (f); and/or

         (h)  any use of (a), (b) or (c).

         The term "Know-How," however, shall not include any know-how,
         processes, information and data which is, as of the Effective Date or
         becomes later on, generally available to the public.

    1.25 "LICENSED COMPOUND" shall mean CO 2-6749 and any Back-Up Compound
         Candidate.

    1.26 "MAA" shall mean the Marketing Authorization Application filed in the
         European Community for approval to market and sell a pharmaceutical
         product, whether by centralized procedure with the Committee for
         Proprietary Medicinal Products or otherwise.

    1.27 "MAJOR MARKET COUNTRIES" shall mean Germany, the United Kingdom, Italy
         and France.


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    1.28 "NDA" shall mean a New Drug Application, as defined in the United
         States Federal Food, Drug and Cosmetic Act and applicable regulations
         promulgated thereunder as amended from time to time.

    1.29 "NET SALES" shall mean proceeds from sales of the Product by either
         Party, its Affiliates or sublicensees, as appropriate, to Third
         Parties, less the sum of (a) and (b) where (a) is a provision,
         determined under generally accepted accounting principles in the
         United States, for [          *          ] and (b) is 
         [          *          ].

         Sales of Product by and between a Party and its Affiliates are not
         sales to Third Parties and shall be excluded from Net Sales
         calculations for all purposes.

    1.30 [     *     ] shall have the meaning set forth in Article 4.1.

    1.31 "NON-SCHEDULED PRODUCT" shall mean a Product to be sold in the RoW
         that has received a designation similar to a "Schedule V" designation
         in the USA, as defined in 21 CFR Part 1308, or no scheduling
         designation in the course of Regulatory Approval from a foreign
         government.

    1.32 "PATENT RIGHTS" shall mean all patents or patent applications, in
         whatever country in the RoW, and all divisionals, continuations,
         continuations-in-part, reissues, extensions, supplementary protection
         certificates and foreign counterparts thereof in the RoW, existing as
         of the Effective Date or filed or issuing during the term of this
         Agreement, at least one claim of which covers:

         (a)  the Licensed Compound;

         (b)  any Back-Up Compound;

         (c)  any Product containing (a) or (b);

         (d)  methods of making any of (a), (b) or (c);

         (e)  any component of (c);

         (f)  any intermediate in the making of any of (a), (b), (c) or (e);

         (g)  any method of using any of (a), (b), (c), (e), or (f); and/or

         (h)  any use of (a), (b) or (c).


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    1.33 "PHASE I," "PHASE II," AND "PHASE III" shall mean the phases of the
         clinical development of pharmaceuticals as defined in the United
         States Federal Food, Drug and Cosmetics Act and/or applicable
         regulations promulgated thereunder, as amended from time to time, or
         any comparable foreign regulations.

    1.34 "PRODUCT" shall mean any pharmaceutical product containing a Licensed
         Compound in any formulation or mode of administration.

    1.35 "REGULATORY APPROVAL" shall mean all authorizations by the competent
         authorities which are required for the regular marketing, promotion,
         pricing and sale of the Product in a given country or regulatory
         jurisdiction.

    1.36 "ROW" shall mean all countries and territories in the world except the
         USA.

    1.37 "ROYALTY TERM" shall mean the period extending from First Commercial
         Sale in any country in the RoW until the later of (i) expiration of
         the last to expire patent within the Patent Rights necessary to make,
         use, import, offer for sale or sell the Product in one or more Major
         Market Countries, or (b) fifteen (15) years from First Commercial Sale
         in the first Major Market Country.

    1.38 "SCHEDULED PRODUCT" shall mean a Product to be sold in the RoW that
         has received a designation similar to a Schedule I, II, III or IV
         designation in the USA, as defined in 21 CFR Part 1308, in the course
         of Regulatory Approval from a foreign government.

    1.39 "THIRD PARTY(IES)" shall mean any person(s) or entity(ies) other than
         CoCensys, Wyeth-Ayerst or their Affiliates.

    1.40 "TRADEMARK" shall mean the trademark under which the Product shall be
         marketed as set out in Article 9.

    1.41 "USA" shall mean the United States of America, its territories and
         possessions and the Commonwealth of Puerto Rico.

    1.42 "WYETH-AYERST PATENT RIGHTS" shall mean all Patent Rights owned or
         Controlled by Wyeth-Ayerst.  A list of the Wyeth-Ayerst Patent Rights
         existing as of the Effective Date is set out in Exhibit E hereto.

2.  DEVELOPMENT OF LICENSED COMPOUND.

    2.1  GENERAL OBLIGATIONS.  Wyeth-Ayerst shall be responsible for the
         design, implementation and funding of all Development.  Wyeth-Ayerst
         agrees to use Commercially Reasonable Efforts to conduct the
         Development with the intent of obtaining Regulatory Approval in the
         RoW and bringing a Product in the Field 


                                       6.
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          to the market as soon as reasonably practicable. Wyeth-Ayerst shall 
          ensure that the Development is carried out adhering to 
          Wyeth-Ayerst's ethical and safety standards.  Wyeth-Ayerst shall 
          have the right to subcontract with third parties any of its 
          Development obligations   hereunder, without the consent or 
          approval of CoCensys.  In the event Wyeth-Ayerst intends to 
          exercise its right to subcontract one or more of its Development 
          obligations, it shall notify CoCensys of such intent and CoCensys 
          shall have the right to submit one or more proposals to 
          Wyeth-Ayerst to perform such one or more parts of such Development  
          activities.  Wyeth-Ayerst shall consider all such proposals 
          submitted by CoCensys on an equal basis with proposals submitted by 
          Third Party subcontractors for the same Development tasks.

     2.2  RECORDS, REPORTS AND INFORMATION EXCHANGE.

          2.2.1     TECHNOLOGY AND INFORMATION TRANSFER. CoCensys will provide 
                    to Wyeth-Ayerst all Know-How as Wyeth-Ayerst deems 
                    necessary to carry out the Development and [     *     ]
                    of the Product and to obtain Regulatory Approval.  All 
                    information transferred, provided or exchanged under this 
                    Article 2.2.1 will be subject to the confidentiality
                    requirements set forth in Article 17.

          2.2.2     RECORD KEEPING.  Wyeth-Ayerst will maintain records in 
                    sufficient detail and in good scientific manner appropriate
                    for Regulatory Approval and patent purposes.

          2.2.3     COMMUNICATION REGARDING THE DEVELOPMENT PROGRESS.  A 
                    project team shall be appointed by Wyeth-Ayerst and 
                    representatives thereof shall meet with representatives of 
                    CoCensys on a regular basis (but no less often than every 
                    six (6) months) to keep CoCensys apprised of the 
                    Development progress and to bring to its attention any 
                    problems or issues which may have an impact on the timing 
                    of the Development (e.g., regulatory submissions).

     2.3  COMPLIANCE.  Wyeth-Ayerst shall comply with all GLP, GCP and GMP in 
          the conduct of the Development.

     2.4  FUNDING OF THE DEVELOPMENT.  Wyeth-Ayerst shall be responsible for 
          one hundred percent (100%) of all costs, fees and expenses 
          associated with the Development and the obtaining of all Regulatory
          Approvals.

     2.5  REGULATORY APPROVALS.  [     *     ] shall file all regulatory 
          dossiers under its name.  [     *     ] shall own all Regulatory 
          Approvals.  [     *     ] shall have the right of reference to the 
          extent necessary to exercise its rights or to meet its


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          obligations hereunder.  [     *     ] shall be responsible for all 
          communications with regulatory agencies.

3.   BACK-UP COMPOUND CANDIDATES
     
      Unless otherwise provided, all of the Parties' rights and obligations 
      under this Agreement, including those regarding the development, 
      manufacture, distribution, marketing, sale, promotion, profit-sharing 
      and royalties of CO 2-6749 and the Product are applicable to any Back-Up 
      Compound Candidate either replacing CO 2-6749 or otherwise developed in 
      the Field pursuant to Agreement (No. 1).  The provisions herein 
      regarding CO 2-6749 and the Product shall apply to such Back-Up Compound 
      Candidate MUTATIS MUTANDIS.

4.   INDICATIONS; EXCLUSIVITY.

     4.1  INDICATIONS.  Wyeth-Ayerst shall have the right to  conduct 
          Development with respect to any Licensed Compound.  Wyeth-Ayerst 
          [   *   ] covenants that it shall not conduct clinical trials of any 
          Licensed Compound for [   *   ] in the Row except as provided under 
          this Article 4.1.  If Wyeth-Ayerst discovers or determines that any 
          Licensed Compound may have efficacy in the treatment of [   *   ] 
          and if Wyeth-Ayerst desires to pursue clinical trials of such Licensed
          Compound [     *     ] it will promptly notify CoCensys in writing and
          disclose to CoCensys its rationale therefor.  Wyeth-Ayerst shall have 
          the right to pursue such clinical trials for [     *     ] and market 
          and sell such Licensed Compound as though it were a Product developed 
          and sold for [   *    ]under this Agreement, subject to the Parties 
          negotiation of terms and conditions, including royalty rates, whether 
          and on what terms such Licensed Compound will be Co-Promoted by the 
          Parties, and other appropriate payment and other terms.  Following 
          such negotiation of such terms and conditions the Parties shall either
          enter into a separate agreement or amend this Agreement to so provide 
          for such terms and conditions.  In the event the Parties are unable to
          come to agreement as to the appropriate terms and conditions for the 
          development and commercialization of such Licensed Compound for 
          [     *     ] by Wyeth-Ayerst, the matter shall be referred to the 
          Chief Executive Officer of CoCensys and the President of Wyeth-Ayerst
          Laboratories, an Affiliate of Wyeth-Ayerst, for good faith 
          resolution, for a period of [    *     ] days.  If such matter is not
          resolved by the end of such [    *     ] day period, the Parties 
          shall be [     *      ]. Notwithstanding the foregoing, it is 
          expressly understood and


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          agreed that [    *     ] as used in this Agreement shall not include 
          [   *    ].
     
     4.2  NO [     *     ] BY COCENSYS [     *     ].  During the term of this 
          Agreement, CoCensys shall not [     *     ]

     4.3  NO [     *     ]  During the term of this Agreement, CoCensys will 
          not [     *     ] except under the terms of this Agreement, or as 
          otherwise agreed to by Wyeth-Ayerst.

5.   LICENSE GRANTS.

     5.1  LICENSES TO WYETH-AYERST.  Subject to the other
          provisions of this Agreement, CoCensys hereby grants to
          Wyeth-Ayerst:

          5.1.1     An exclusive license in the RoW, under its Intellectual 
                    Property Rights, to develop, manufacture and have
                    manufactured, import, use, market, offer for sale and sell 
                    Products, in the Field, and, subject to Article 4.1, for
                    any New Indication.

          5.1.1     The licenses granted in Article 5.1.1 shall be 
                    sublicensable by Wyeth-Ayerst outside the USA without 
                    the consent of CoCensys to Affiliates and Third Parties.  
                    Wyeth-Ayerst agrees to keep CoCensys informed as to such
                    sublicensing activities.

          5.1.2     Unless otherwise provided in this Agreement, Wyeth-Ayerst 
                    covenants that it shall not, nor shall it cause any 
                    Affiliate to, use or practice directly or indirectly any 
                    CoCensys Know-How, and, until expiration thereof, any
                    CoCensys Patent Rights for any purposes other than the 
                    development, manufacture, importation, use, marketing, offer
                    for sale or sale of the Product.

          5.1.3     Wyeth-Ayerst may at any time request and authorize CoCensys
                    to grant licenses directly to Affiliates of Wyeth-Ayerst 
                    wheresoever located by giving written notice to CoCensys
                    designating to whom a direct license is to be granted by 
                    CoCensys.  CoCensys shall promptly enter into a separate 
                    direct license agreement with each Affiliate of Wyeth-Ayerst
                    designated by Wyeth-Ayerst in such notice. All such direct 
                    license agreements shall be consistent with the terms of 
                    this Agreement, to the extent applicable, except for such
                    modifications as may be required by the laws, regulations 
                    and customs in the country in which the direct license 
                    agreement is to be performed.


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      5.2  LICENSES UPON EXPIRATION.  Upon expiration of the Royalty Term, 
           and provided all sums owing to CoCensys have been paid, 
           Wyeth-Ayerst shall have a [     *      ] where agreed under Article 
           4.1, under any remaining CoCensys Intellectual Property Rights.

6.   CONSIDERATION TO COCENSYS.

     6.1  PAYMENTS.  In further consideration of CoCensys' continuing 
          assistance in research and development of the Product, Wyeth-Ayerst 
          shall pay to CoCensys the following amounts at the time of the 
          following achievements with respect to the Product:

          6.1.1     [    *     ]  Upon [     *     ] Wyeth-Ayerst shall make to
                    CoCensys a non-refundable payment of [      *       ].

          6.1.2     [          *          ]  Upon [     *      ] 
                    Wyeth-Ayerst shall make to CoCensys a non-refundable payment
                    of [         *        ].

          6.1.3     [          *        ]  Upon [      *       ] Wyeth-Ayerst 
                    shall make to CoCensys a non-refundable payment of 
                    [   *   ]if the Product is a [   *  ] Product in such 
                    [   *   ], or [   *   ] if the Product is a [  *  ]
                    Product in such [   *   ].  If the Product is a [   *   ] 
                    Product in all [   *   ] Wyeth-Ayerst shall make to 
                    CoCensys an additional non-refundable payment of 
                    [   *     ].

          6.1.4     [     *     ]  Upon [          *          ]
                    Wyeth-Ayerst shall make to CoCensys a non-refundable payment
                    of [  *   ] if the Product is a [     *     ] Product or
                    [  *  ] if the Product is a [     *      ] Product.

     6.2  METHOD OF PAYMENT OF PAYMENTS.  All payments shall be made  by 
          Wyeth-Ayerst to CoCensys by way of wire transfer to CoCensys 
          within thirty (30) days from the date corresponding to the event 
          triggering the milestone payment.


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     6.3  PAYMENTS FOR BACK-UP COMPOUND CANDIDATES.  Each payment payable 
          pursuant to this Article 6 shall [     *     ] be payable 
          [     *     ] for the Product [     *     ].

     6.4  ROYALTIES AND PROFIT SHARING.  Wyeth-Ayerst shall, in addition to 
          the payments set forth above, also pay to CoCensys royalties and 
          such other amounts as set forth in Article 7.

7.   MARKETING AND ROYALTIES IN THE ROW.

     7.1  MARKETING BY WYETH-AYERST.  Wyeth-Ayerst shall have exclusive rights 
          to the Product in the countries of the RoW, and shall use 
          Commercially Reasonable Efforts to market, sell and distribute the 
          Product at its discretion in such countries through its own network
          and direct licensee Affiliates, and/or through the network of its 
          licensees/distributors, subject to Article 5.1.2.

     7.2  COMMERCIAL AND REGULATORY DILIGENCE.

          7.2.1     Within [     *     ] months of [     *     ] for the Product
                    in the USA or the European Union, Wyeth-Ayerst will commence
                    [     *      ] and notify CoCensys in writing of such event.

          7.2.2     Within [     *     ] months of [    *    ] Wyeth-Ayerst 
                    shall notify CoCensys in writing as to [         *        ].

          7.2.3     After [          *          ] Wyeth-Ayerst agrees that it 
                    will undertake commercial launch of the Product in such 
                    country [         *          ].

     7.3  ANNUAL NET SALES CALCULATIONS.  Annual Net Sales in the RoW of 
          [     *     ] and [     *     ] Products shall be first calculated on
          a country-by-country basis until the end of the Royalty Term.  Then 
          Net Sales of [     *    ] Products in all countries in the RoW shall 
          be added together to calculate annual Net Sales of [     *    ] 
          Products in the RoW; and Net Sales of [     *    ] Products in all 
          countries in the RoW shall be added together to calculate annual 
          Net Sales of [     *     ] Products in the RoW.  Finally, Net Sales 
          of [     *    ] Products and Net Sales of [     *     ] Products 
          shall be added together to calculate annual RoW Net Sales.


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     7.4  [     *     ] PRODUCT ROYALTY IN THE ROW.  In consideration of the 
          licenses granted to Wyeth-Ayerst by CoCensys under Article 5, 
          Wyeth-Ayerst shall pay to CoCensys a running royalty on annual Net 
          Sales of all [     *     ] Products in the RoW according to the
          following marginal rates:

          (a)  For annual RoW Net Sales which are less than or equal to [  *  ]
               million, [     *     ] of such RoW Net Sales which are allocable
               to Net Sales of [     *     ] Products; and

          (b)  For annual RoW Net Sales which are more than [    *     ] million
               but less than or equal to [    *    ] million, 
               [     *     ] of such RoW Net Sales which are allocable to Net 
               Sales of [   *   ] Products; and

          (c)  For annual RoW Net Sales which are more than [   *   ] million, 
               [   *   ] of such RoW Net Sales which are allocable to Net Sales
               of [   *   ] Products.

     7.5  [     *     ] PRODUCT ROYALTY.  In consideration of the licenses    
          granted to Wyeth-Ayerst by CoCensys under Article 5, Wyeth-Ayerst 
          shall pay to CoCensys a running royalty on Net Sales of all [   *   ]
          Products in the RoW according to the following marginal rates:

          (a)  For annual RoW Net Sales which are less than or equal to 
               [   *   ] million, [     *     ] of such RoW Net Sales which are
               allocable to Net Sales of [     *     ] Products; and

          (b)  For annual RoW Net Sales which are more than [  *   ] million 
               but less than or equal to [    *    ] million, [     *     ] of
               such RoW Net Sales which are allocable to Net Sales of 
               [    *    ] Products; and

          (c)  For annual RoW Net Sales which are more than [   *     ] million,
               [     *     ] of such RoW Net Sales which are allocable to Net 
               Sales of [    *   ] Products.


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     7.6  PAYMENTS.  All royalties payable to CoCensys under this Article 7
          shall be paid in U.S. Dollars within three (3) months after
          the close of each calendar quarter, or earlier if possible, during the
          Royalty Term.  Each payment shall be accompanied by a statement, on a 
          country by country basis, of the amount of Net Sales in the RoW during
          such quarter, the aggregate amount of Net Sales for the year-to-date 
          in the RoW, and amount of royalties due on such Net Sales.  For any 
          given royalty period during the first three (3) quarters of the year,
          Wyeth-Ayerst shall pay to CoCensys the royalty at the lowest rate 
          specified in Articles 7.4 and 7.5 applicable to the then current 
          year-to-date worldwide RoW Net Sales level. Each statement provided at
          the end of the fourth quarter shall contain a reconciliation of actual
          royalty payments made during that year, any adjustments to be made to 
          such royalty    amounts owing for such year, and the amount actually 
          owed for such year.  Any amounts owing to CoCensys shall be paid to 
          CoCensys at the time of such fourth quarter statement, in accordance 
          with the terms of this Article 7.6.  Any adjustments to royalties owed
          in the RoW pursuant to Articles 7.7.1 and 7.7.2 shall be done at the 
          end of the calendar year in which such event giving rise to such 
          adjustment occurred; PROVIDED, HOWEVER, that following the entry of 
          one or more generic products in any year, and where royalties were 
          reduced for that year pursuant to Article 7.7.1, the following year's
          royalty rate for quarterly royalty payments shall be at [     *     ]
          with a reconciliation upward at year end in the event sales of such
          generic product(s) do not rise to the level specified in 
          Article 7.7.1.
               
     7.7  ADJUSTMENT TO ROYALTIES IN ROW.
               
          7.7.1     GENERIC PRODUCTS.  In the event that, during the Royalty 
                    Term, a generic version of the Product is introduced in 
                    any country in the RoW by a Third Party, and if unit sales 
                    of all such generic product(s) constitute more than [   *  ]
                    of the combined unit sales in the RoW of both the Product 
                    and any such generic product(s), then the annual royalty
                    amount owed under Article 7.4 or 7.5 for such country shall
                    be reduced by [   *    ] such reduction to be done 
                    in the fourth quarter payment as described in Article 7.6.

          7.7.2     [     *     ]  In the event that at the end of a given 
                    calendar year [     *     ] (where [     *     ] = 
                    [          *          ] = the [       *       ] and 
                    [     *     ] = [     *     ] then Wyeth-Ayerst will provide
                    written notice to CoCensys of such fact and the Parties 
                    shall meet promptly thereafter to discuss and develop in 
                    good faith a commercially reasonable plan to [     *      ]
                    In the event that, at any time after the eight (8) month 
                    anniversary of the date of the first meeting to discuss the 
                    RoW 


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                    Cost Reduction Plan, [     *     ] (where [   *   ] = 
                    [     *     ] then, for so long as [    *     ] an amount 
                    equal to [     *     ] may be deducted from the royalty 
                    amount due CoCensys for such year; PROVIDED, HOWEVER, in
                    no event shall the royalty due CoCensys be less than that 
                    paid at the lowest applicable rate (i.e., [     *     ] 
                    for [     *     ] Products and [     *     ] for [    *    ]
                    Products, or [     *     ] respectively, where 
                    Article 7.7.1 applies) set forth in Article 7.4 or 7.5.

8.   ACCOUNTS AND RECORDS; WITHHOLDING TAX.

     8.1  RECORDS.  Wyeth-Ayerst shall keep accurate books and accounts 
          of record in connection with the manufacture, use and/or sale by or
          for it of the Products in sufficient detail to permit accurate 
          determination of all figures necessary for verification of royalties,
          profits, milestone payments and other compensation required to be
          paid hereunder. Wyeth-Ayerst shall maintain such records for a period
          of three (3) years after the end of the year in which they were 
          generated.

     8.2  AUDITS.  CoCensys, through an independent certified public accountant
          reasonably acceptable to Wyeth-Ayerst, shall have the right, at its 
          own expense, to access the books and records of Wyeth-Ayerst for the 
          sole purpose of verifying statements furnished by Wyeth-Ayerst 
          pursuant to Article 7.6.  Such access shall be conducted after 
          reasonable prior written notice to Wyeth-Ayerst and during ordinary 
          business hours and shall not be more frequent than once during each 
          calendar year.  CoCensys agrees to keep in strict confidence all 
          information learned in the course of such audit, except when it is 
          necessary to reveal such information in order to enforce its rights 
          under this Agreement.  CoCensys' right to have such records examined 
          shall survive termination or expiration of this Agreement.  In the 
          event such audit reveals an underpayment of [     *     ] or more of 
          the amount actually due, Wyeth-Ayerst shall reimburse CoCensys for 
          the costs of such audit in addition to promptly remitting to CoCensys
          the amount of any underpayment.
     
     8.3  FOREIGN EXCHANGE.  For the purpose of computing Net Sales for Products
          sold in a currency other than United States Dollars, such currency 
          shall be converted into United States Dollars in accordance with 
          Wyeth-Ayerst's customary and usual translation procedures, 
          consistently applied.

     8.4  SALES BY SUBLICENSEES.  In the event Wyeth-Ayerst grants 
          licenses or sublicenses to others to make or sell the Product, such 
          licenses or sublicenses shall include an obligation for the licensee 
          or sublicensee to account for and report its Net Sales of such 
          Products on the same basis as if such sales were Net Sales by 


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          Wyeth-Ayerst, and CoCensys shall receive royalties in the same amounts
          as if the Net Sales of the licensee or sublicensee were Net Sales 
          of Wyeth-Ayerst.
     
     8.5  CURRENCY BLOCKAGE.  In the event Wyeth-Ayerst is prevented from 
          making any payment under this Agreement by virtue of the Statutes,
          Laws, Codes or Governmental Regulations of the country from which 
          the payment is to be made, then such payments may be paid by 
          depositing them in the currency in which accrued to CoCensys'
          account in a bank acceptable to CoCensys in the country whose currency
          is involved.  If the Statutes, Laws, Codes or Governmental Regulations
          prohibit both transmittal and deposit of such payments, the obligation
          to pay, deposit, accrue or otherwise account for such payments in such
          country shall be suspended for so long as said prohibition shall be 
          in effect.

     8.6  WITHHOLDING.  All taxes, assessments and fees of any nature levied 
          or incurred on account of any payments accruing under this Agreement,
          by national, state or local governments, will be assumed and paid by 
          Wyeth-Ayerst, except taxes levied thereon as income to CoCensys and 
          if such taxes are required to be withheld by Wyeth-Ayerst they will 
          be deducted from payments due to CoCensys and will be timely paid by 
          Wyeth-Ayerst to the proper taxing authority for the account of 
          CoCensys, a receipt or other proof of payment therefor secured and 
          sent to CoCensys as soon as practicable.

9.   TRADEMARKS.

     [     *     ] shall select and own the Trademarks for marketing the Product
     in the RoW.  [     *     ] for (i) registration of such Trademarks and 
     (ii) bringing, maintaining and prosecuting any action to protect or defend
     such Trademarks shall be borne [     *     ]  At the termination of this 
     Agreement, [     *     ] shall [     *     ] have unrestricted ownership 
     of such Trademark(s) in the RoW.  

10.  MANUFACTURING AND DISTRIBUTION.

     10.1 PRIMARY MANUFACTURE.  [     *     ] shall manufacture or have 
          manufactured its requirements for clinical and commercial supplies 
          of the Product.  In fulfilling its manufacturing obligations 
          hereunder, [     *     ] will use at least the same level of effort 
          as it employs for its other products of similar scientific and 
          commercial promise.  If [     *     ] elects to have the Product
          manufactured, [     *     ] shall favorably consider using, but shall
          not be obligated to use, [     *    ] as its manufacturing 
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     10.2 SECOND SOURCE.  In order to ensure an uninterrupted supply of 
          the Product, the Parties intend to identify a Third Party manufacturer
          (the "Second Source") to manufacture the Product in the event that 
          [     *     ]is unable to supply all of the reasonably anticipated 
          requirements of the Product.  If the Second Source manufactures the 
          Product pursuant to this Article 10.2, Wyeth-Ayerst and CoCensys shall
          cooperate and assist each other to obtain, transfer or use any 
          licenses, registrations or information reasonably required to permit 
          such Second Source to manufacture the Product.
     
     10.3 EXCHANGE OF INFORMATION.  Subject to Article 17, the Parties 
          undertake to exchange and to use diligent efforts to cause Third Party
          manufacturers to exchange, on a regular basis, all data and know-how 
          relating to the manufacture of the Product.

     10.4 COMPLIANCE.  Any manufacture of the Product for sale in the 
          RoW shall be performed in full compliance with all applicable foreign
          GMP and applicable laws and regulations.  CoCensys shall be entitled 
          to audit such compliance and in particular the quality assurance 
          program for the manufacture of the Product.

11.  PROSECUTION, MAINTENANCE AND INFRINGEMENT OF INTELLECTUAL
     PROPERTY RIGHTS.

     11.1 PATENTABLE INVENTIONS.

          11.1.1    Wyeth-Ayerst shall own all Inventions made solely by its 
                    employees and agents, and all patent applications and 
                    patents claiming such Inventions.  CoCensys shall own all 
                    Inventions made solely by its employees and agents, and all
                    patent applications and patents claiming such Inventions.  
                    All Inventions made jointly by employees or agents of 
                    CoCensys and employees or agents of Wyeth-Ayerst and all 
                    patent applications and patents claiming such Inventions 
                    shall be owned jointly by CoCensys and Wyeth-Ayerst. All 
                    determinations of inventorship under this Article 11.1.1 
                    shall be in accordance with U.S. law.

          11.1.2    Wyeth-Ayerst and CoCensys shall each disclose to the other 
                    and discuss any Inventions and the desirability of filing a
                    United States patent application covering the Invention, as
                    well as any foreign counterparts.  The Party owning the 
                    Invention shall make the final decision with respect to any
                    such filings. With respect to jointly owned Inventions, the
                    Parties shall determine which Party shall file and prosecute
                    any patent applications thereon.  [     *     ] shall be 
                    responsible for expenses for preparing and prosecuting joint
                    patent applications in the RoW.


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          11.1.3    Each Party shall have the right to select patent counsel and
                    to take such other actions as are reasonably appropriate to
                    prepare, file, prosecute and maintain patent protection with
                    respect to its Inventions arising under this Article 11.1.

     11.2 PROSECUTION AND MAINTENANCE OF PATENT RIGHTS.  Each Party 
          shall be responsible for prosecuting and maintaining its own Patent 
          Rights, subject to Article 11.1.2.  With respect to the RoW, the 
          decision as to whether to prosecute and maintain Patent Rights, and in
          which countries to do so, shall be made jointly by Wyeth-Ayerst and 
          CoCensys.  To facilitate such decision-making, each Party will appoint
          a "patent coordinator", who will have the authority to make such 
          decision on behalf of such Party.  All expenses for filing, 
          prosecuting and maintaining the CoCensys Patent Rights in the RoW 
          shall be paid by [    *    ].

     11.3 PATENT EXTENSIONS.  The Party holding a Patent Right, if requested by
          and with the assistance of the other Party, shall apply in a timely 
          manner for such patent term extensions or patent restoration 
          certificates for such Patent Right as are available under similar
          legislation to the U.S. Federal Drug Price Competition and Patent 
          Term Restoration Act of 1984 (Pub. L. No. 98-417), and any amendments
          thereof or any successor acts thereto. [     *     ] expenses incurred
          in connection with such patent term extensions or patent restoration 
          certificates shall be borne [     *      ].

     11.4 COOPERATION.  Each of the Parties shall execute or have 
          executed by its appropriate employees, representatives, agents, and 
          contractors such documents as may be necessary to obtain, perfect or 
          maintain any Patent Rights filed or to be filed pursuant to this 
          Agreement, and to cooperate with the other Party so far as reasonably 
          necessary with respect to furnishing all information and data in its 
          possession reasonably necessary to obtain or maintain such Patent 
          Rights.

     11.5 INFRINGEMENT OF INTELLECTUAL PROPERTY RIGHTS.

          11.5.1

               (a)  If either Party should become aware of any infringement or 
                    threatened infringement or misappropriation, as the case 
                    may be, in the RoW of any Intellectual Property Rights of
                    the other Party, it shall promptly notify such other Party 
                    in writing.  As soon as practicable the Parties shall 
                    confer on the particulars of such infringement or 
                    misappropriation and the possible courses of  action to be 
                    taken.  The Party holding the affected Intellectual Property
                    Rights shall have the right, but not the obligation, to
                    institute, prosecute and control any 


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         legal proceedings in its own name and by its own counsel and at its 
         own expense, subject to Article 11.5.1(d), to prevent or restrain 
         such infringement, and the other Party shall have the right, 
         [     *     ] to be represented in such action by its own counsel.  
         If one Party brings any such action or proceeding, the other Party 
         hereby consents to being joined as a party plaintiff where 
         necessary and, in case of joining, such other Party agrees to give 
         the first Party reasonable assistance and authority to file and to 
         prosecute such suit, at the exercise of the Party bringing such 
         suit.

   (b)   Notwithstanding the foregoing, the Parties shall jointly determine 
         which Party shall have the primary right and responsibility (but 
         not the obligation) to institute, prosecute, and control any action 
         or proceeding with respect to infringement or misappropriation of 
         jointly owned Intellectual Property Rights in the RoW and the other 
         Party shall have the right [     *    ] to be represented by its 
         counsel.  Each Party hereby consents to the filing of any such 
         action by the other Party with respect to any jointly owned Patent 
         Rights in accordance with this Article 11.5.1(b).

   (c)   If one Party alone prosecutes an infringement or misappropriation of 
         Intellectual Property Rights, [          *          ] any damages 
         and costs recovered in any proceedings or by way of settlement 
         under Articles 11.5.1(a) and 11.5.1(b) above or Article 11.5.2 
         shall [         *          ] as applicable.

   (d)   If both Parties participate in prosecuting an infringement or 
         misappropriation of Intellectual Property Rights, the actual costs 
         and expenses of all suits brought by either Party under this 
         Article 11.5.1 shall be [          *          ].  Any remaining 
         damages shall then be [          *         ].

11.5.2   If the Party having the primary right to institute, prosecute, and 
         control such infringement or misappropriation action under Article 
         11.5.1 fails to do so within a period of one hundred twenty (120) 
         days after receiving notice of the infringement, or if that Party, 
         after initiating an action, determines to discontinue such action, 
         the other Party shall have the right to bring and control or take 
         over any such action by counsel of its own choice, and at its own 
         expense, subject to Article 11.5.1(c) unless prevented from doing 
         so by the laws of the country where the infringement or 
         misappropriation occurred or is threatened.
         

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     11.5.3   In connection with any proposed settlement in respect of any 
              infringement or threatened infringement of any Intellectual 
              Property Rights, the Party intending to settle shall notify 
              and consult with the other Party as to the terms of 
              settlement, whose written consent shall be required prior to 
              any such settlement, such consent shall not be unreasonably 
              withheld.
         
     11.5.4   In connection with any action taken by either Party against a 
              Third Party to protect or enforce any Intellectual Property 
              Rights, the other Party shall, if requested, consult with the 
              Party taking such action, and make available as witnesses its 
              employees or as evidence any materials, and/or data as are 
              reasonably necessary for the furtherance of such action.  The 
              expenses in connection with the providing of witnesses and/or 
              the making available of any materials and/or data shall be 
              [          *          ].
         
11.6 INFRINGEMENT OF THIRD PARTY PATENT RIGHTS.

     11.6.1   If Wyeth-Ayerst should be of the opinion that it cannot make, 
              import, use, market and/or sell the Product in the RoW under 
              its own Intellectual Property Rights or those licensed to it 
              by CoCensys under this Agreement without infringing a Third 
              Party's patent, it shall notify CoCensys.  Both Parties then 
              shall seek an opinion of patent counsel acceptable to both 
              Parties.  If such patent counsel concurs with Wyeth-Ayerst's 
              opinion, they shall jointly or independently endeavor to 
              secure a license from the Third Party on terms that are 
              acceptable to both Parties.

     11.6.2   If, in the opinion of patent counsel selected under Article 
              11.6.1, the Third Party patent, if litigated, would be found 
              invalid or not be infringed by the manufacture or sale of the 
              Product or if the Parties otherwise mutually agree to obtain a 
              license to such Third Party patent, the Parties shall proceed 
              in accordance with the terms of this Agreement, unless an 
              action for infringement is brought against one or both Parties.

     11.6.3   If either Party is sued for patent infringement of any Third 
              Party patents arising out of the manufacture, use, sale or 
              importation of the Product in the RoW, the Parties shall 
              promptly meet to discuss the course of action to be taken to 
              resolve or defend any such infringement litigation. Each Party 
              shall provide the other with such assistance as is reasonably 
              necessary and shall cooperate in the defense of any such 
              action.  [     *     ] of any cost/expense of defending such 
              action incurred by Wyeth-Ayerst in a given country 


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                    and any damages and/or other compensation imposed on 
                    Wyeth/Ayerst in such country may be deducted by 
                    Wyeth-Ayerst from any amounts otherwise due CoCensys 
                    under this Agreement in the form of royalties for such 
                    country, PROVIDED, HOWEVER, in no event shall royalty 
                    amounts due CoCensys for such country be reduced by more 
                    than [     *     ]in any given calendar year as a result 
                    of this sentence.
                            
12.  FORCE MAJEURE.

     Neither Party shall be liable to the other for delay or failure in the 
     performance of the obligations on its part contained in this Agreement 
     if and to the extent that such failure or delay is due to circumstances 
     beyond its control which it could not have avoided by the exercise of 
     reasonable diligence.  It shall notify the other Party promptly should 
     such circumstances arise, giving an indication of the likely extent and 
     duration thereof, and shall use all commercially reasonable efforts to 
     resume performance of its obligations as soon as practicable.

13.  TERM AND TERMINATION.

     13.1 GENERAL CONDITIONS OF EXPIRATION AND TERMINATION.

          13.1.1    Any permitted sublicenses granted hereunder shall 
                    automatically terminate or expire at the same time as 
                    this Agreement expires (insofar as they haven't already 
                    terminated), except where, and to the extent, any license 
                    granted hereunder survives expiration of this Agreement, 
                    as expressly provided in this Agreement.  Upon early 
                    termination of this Agreement for any reason, if any 
                    permitted sublicensee is not then in default under its 
                    sublicense agreement with Wyeth-Ayerst, then such 
                    sublicensee shall automatically have a license under this 
                    Agreement as a direct licensee of CoCensys, on economic 
                    terms as are set forth herein with respect to 
                    Wyeth-Ayerst and otherwise with the same rights and 
                    obligations as Wyeth-Ayerst under this Agreement.
                    
          13.1.2    The provisions of Articles 8, 9, 11, 14, 15, and 17 shall 
                    survive termination or expiration of this Agreement.

          13.1.3    Termination or expiration of this Agreement
                    shall not operate to deprive either Party of any rights 
                    or remedies either at law or in equity or to relieve 
                    either Party of any of its obligations incurred prior to 
                    the effective date of such termination or expiration.


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13.2 TERM.  Unless earlier terminated as set out in this Agreement, the term 
     of this Agreement shall end when all the respective royalty payment 
     obligations of the Parties under this Agreement have expired.

13.3 TERMINATION FOR BREACH.

     13.3.1    TERMINATION FOR BREACH.  Except as otherwise provided in this
               Section 13.3.1, either Party may terminate this Agreement for
               material breach by the other Party, which breach remains 
               uncured for [     *     ] in the case of nonpayment of any 
               amount due and [     *    ] for all other breaches, each 
               measured from the date written notice of such breach is given
               to the breaching party, or, if such breach is not susceptible 
               of cure within such [     *     ] period and the breaching 
               party uses diligent good faith efforts to cure such breach, 
               for [     *     ] after written notice to the breaching party.

     13.3.2    BREACH BY WYETH-AYERST.  If termination is due to a material 
               breach by Wyeth-Ayerst, all rights granted to Wyeth-Ayerst
               under this Agreement shall revert to CoCensys, provided that
               [          *          ] as of the date of such termination.

13.4 NO LIMIT ON REMEDIES.  Nothing herein shall exclude or limit any remedies 
     or entitlements whatsoever which the law confers to either Party in the 
     event of a breach of contractual obligations by the other Party.

13.5 UNILATERAL TERMINATION BY WYETH-AYERST.  Wyeth-Ayerst shall have the right 
     to unilaterally terminate this Agreement upon [     *     ] written 
     notice.  In the event of such termination by Wyeth-Ayerst, all 
     Wyeth-Ayerst's rights to the Licensed Compound and the Product in the 
     RoW shall revert to CoCensys.  Wyeth-Ayerst shall not be obligated to 
     make any payments under this Agreement for events which occur after the 
     effective date of such termination.  After the termination date, 
     Wyeth-Ayerst will make its relevant personnel, relevant data and other 
     resources available as are reasonably necessary to effect an orderly 
     transition of Development and commercialization of the Product for a 
     period of [     *     ] after termination.  In the event of such 
     termination, Wyeth-Ayerst shall (i) [          *          ] (ii) 
     [         *          ] and (iii) [          *          ].

13.6 AUTOMATIC TERMINATION OF AGREEMENT (NO. 1).  This Agreement shall 
     terminate automatically if Agreement (No. 1) is terminated for any 
     reason other than expiration or for material breach by CoCensys.


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14.  ASSIGNMENT.

     14.1 ASSIGNMENT TO AFFILIATES.  Either Party may assign any of its rights 
          or obligations under this Agreement in any country to any 
          Affiliates, for so long as they remain Affiliates; provided, 
          however, that such assignment shall not relieve the assigning Party 
          of its responsibilities for performance of its obligations under 
          this Agreement.
          
     14.2 OTHER PERMITTED ASSIGNMENT.  Either Party may assign its rights or 
          obligations under this Agreement in connection with a merger or 
          similar reorganization or the sale of all or substantially all of 
          its assets, [         *          ] provided, that in the event of 
          such merger, reorganization or sale, [          *          ] All 
          other assignments by any Party shall [          *         ].
          
     14.3 BINDING NATURE OF ASSIGNMENT.  This Agreement shall be binding upon 
          and inure to the benefit of the successors and permitted assigns of 
          the Parties.  Any assignment not in accordance with this Article 14 
          shall be void.
          
15.  INDEMNIFICATION.

     15.1 CROSS INDEMNIFICATION.

          15.1.1    Each Party hereby agrees to save, defend and hold the other 
                    Party and its agents and employees harmless from and 
                    against any and all suits, claims, actions, demands, 
                    liabilities, expenses and/or losses, including reasonable 
                    legal expense and attorneys' fees, brought by a Third 
                    Party or that arise in connection with any claim brought 
                    by a Third Party ("Losses") resulting directly from the 
                    manufacture, use, handling, storage, sale or other 
                    disposition of Products in the RoW to the extent such 
                    Losses result solely from (i) the negligence of the 
                    indemnifying party or breach by the indemnifying party of 
                    any provision of this Agreement, (ii) failure of the 
                    indemnifying party to manufacture or have manufactured 
                    Products (bulk or finished  form) according to cGMP or 
                    Product specifications, or (iii) marketing activities of 
                    the indemnifying party contrary to applicable 
                    governmental regulations or outside the approved labeling 
                    of the Product.
                    
          15.1.2    In the event CoCensys is seeking indemnification under 
                    Article 15.1.1, it shall inform Wyeth-Ayerst of a claim 
                    as soon as is reasonably practicable after it receives 
                    notice of the claim, shall permit Wyeth-Ayerst to assume 
                    direction and control of the defense of the claim 
                    (including the right to settle the claim solely for 
                    monetary 


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                    consideration), and shall cooperate as requested (at the 
                    expense of Wyeth-Ayerst) in the defense of the claim.

          15.1.3    In the event Wyeth-Ayerst is seeking indemnification under 
                    Article 15.1.1, it shall inform CoCensys of a claim as 
                    soon as is reasonably practicable after it receives 
                    notice of the claim, shall permit CoCensys to assume 
                    direction and control of the defense of the claim 
                    (including the right to settle the claim solely for 
                    monetary consideration), and shall cooperate as requested 
                    (at the expense of CoCensys) in the defense of the claim.
                    
     15.2 INSURANCE.  Each Party further agrees to use reasonable commercial 
          efforts to obtain and maintain, during the term of this Agreement, 
          Comprehensive General Liability Insurance, including Products 
          Liability, with reputable and financially secure insurance carriers 
          or self-insurance, with limits of not less than $5,000,000 per 
          occurrence and in the aggregate to cover its indemnification 
          obligations under Articles 15.1 and 15.2.

16.  WARRANTIES AND REPRESENTATIONS.

     16.1 GENERAL.  Each Party hereby warrants to the other:

          16.1.1    that it has full power and authority to execute and deliver 
                    this Agreement and to perform the obligations on its part 
                    hereunder; and

          16.1.2    that the execution and delivery by it of this Agreement and 
                    the performance of its obligations hereunder have been 
                    duly approved by all necessary corporate action and do 
                    not require any shareholder action or approval.

          16.1.3    that, to the best of its knowledge, the manufacture, use, 
                    importation, offer for sale, or sale of CO 2-6749 will 
                    not infringe any Third Party patent in the RoW.

17.  CONFIDENTIAL INFORMATION.

     17.1 INFORMATION.  Each Party shall keep all information received from 
          the other Party (the "Information") confidential and shall not 
          disclose nor use the Information without the other Party's written 
          consent except to the extent contemplated by this Agreement. This 
          restriction shall not, however, prevent disclosure of the 
          Information if and to the extent that disclosure is required by 
          law, PROVIDED THAT the disclosing Party informs the other Party 
          without delay of any such 


                                       23.

<PAGE>

          requirement, in order to allow such other Party to object to such 
          disclosure and to seek an appropriate protective order or similar 
          protection prior to disclosure.
    
    17.2  EXCEPTIONS.  The above obligations shall not apply or shall cease to
          apply to Information which:
    
          17.2.1    is now, or hereafter becomes, through no act or failure to
                    act on the part of the receiving Party, generally known or
                    available;
    
          17.2.2    is known by the receiving Party at the time of receiving
                    such information, as evidenced by its written records;
    
          17.2.3    is hereafter furnished to the receiving Party by a Third
                    Party, as a matter of right and without restriction on
                    disclosure;
    
          17.2.4    is independently developed by or for the receiving Party
                    without any breach of this Article 17; or
    
          17.2.5    is the subject of a written permission to disclose provided
                    by the disclosing Party.
    
    17.3  PERMITTED DISCLOSURES.  Information may be disclosed to employees,
          agents, consultants, sublicensees or suppliers of the recipient Party
          or its Affiliates, but only to the extent required to accomplish the
          purposes of this Agreement and only if the recipient Party obtains
          prior agreement from its employees, agents, consultants, sublicensees
          or suppliers to whom disclosure is to be made to hold in confidence
          and not make use of such information for any purpose other than those
          permitted by this Agreement. Each Party will use at least the same
          standard of care as it uses to protect proprietary or confidential
          information of its own to ensure that such employees, agents,
          consultants, sublicensees or suppliers do not disclose or make any
          unauthorized use of the Information.
    
    17.4  DISCLOSURE OF AGREEMENT.  Neither CoCensys nor Wyeth-Ayerst shall
          release to any Third Party or publish in any way any non-public
          information with respect to the terms of this Agreement or concerning
          their cooperation without the prior written consent of the other,
          which consent will not be unreasonably withheld or delayed; provided;
          however that either Party may disclose the terms of this Agreement to
          the extent required to comply with applicable laws, including without
          limitation the rules and regulations promulgated by the Securities and
          Exchange Commission and the Party intending to disclose the terms of
          this Agreement shall provide the nondisclosing party an opportunity to
          review and comment on the intended disclosure which is reasonable
          under the circumstances.  Notwithstanding any other provision of this
          Agreement, each Party may disclose the terms of this Agreement to
          lenders, investment bankers and other financial
    
    
                                         24.
    
<PAGE>

          institutions of its choice solely for purposes of financing the
          business operations of such Party either (i) upon the written consent
          of the other Party or (ii) if the disclosing Party uses reasonable
          efforts to obtain a signed confidentiality agreement with such
          financial institution with respect to such information, upon terms
          substantially similar to those contained in this Article 17.
    
    17.5  PUBLICITY.  Subject to Section 17.4, all publicity, press releases and
          other announcements relating to this Agreement or the transaction
          contemplated hereby shall be reviewed in advance by, and shall be
          subject to the approval of, both Parties.
    
    17.6  PUBLICATION.  The Parties shall cooperate in appropriate publication
          of the results of research and development work performed pursuant to
          this Agreement, but subject to their predominating interest in
          obtaining patent protection for any patentable subject matter.  The
          determination of authorship for any paper shall be in accordance with
          accepted scientific practice.  Notwithstanding anything in this
          Article 17.6 to the contrary, all publication and presentations of the
          results of research and development work performed pursuant to this
          Agreement must be approved in advance by both Parties.
    
18.   MISCELLANEOUS.
    
    18.1  NO WAIVER OF CONTRACTUAL RIGHTS.  The failure of either Party to 
          require performance by the other Party of any of that other Party's 
          obligations hereunder shall in no manner affect the right of such
          Party to enforce the same at a later time. No waiver by any Party
          hereto of any  condition, or of the breach of any provision, term,
          representation or warranty contained in this Agreement, whether by
          conduct or otherwise, in any one or more instances, shall be deemed
          to be or construed as a further or continuing waiver of any such
          condition or breach, or of any other condition or of the breach of any
          other provision, term representation or warranty hereof.

    18.2  EXECUTION AND AMENDMENTS.

          18.2.1    Each Party shall execute and deliver all such instruments
                    and perform all such other acts as the other Party may
                    reasonably request in order to carry out the transactions
                    contemplated by this Agreement.

          18.2.2    This Agreement may not be amended or modified except by
                    written instrument signed by or on behalf of both Parties.


    18.3  SEVERABILITY.  If a court or other tribunal of competent jurisdiction
          should hold any term or provision of this agreement to be excessive,
          or invalid, void or unenforceable, the offending term or provision
          shall be deleted, and, if possible,


                                      25.
<PAGE>

          replaced by a term or provision which, so far as practicable achieves
          the legitimate aims of the Parties.

    18.4  RELATIONSHIP BETWEEN THE PARTIES.  Both Parties are independent
          contractors under this Agreement.  Nothing contained in this Agreement
          is intended nor shall be construed so as to constitute CoCensys or
          Wyeth-Ayerst as partners or joint venturers with respect to this
          Agreement.  Neither Party shall have the express or the implied right
          nor authority to assume or create any obligations on behalf of or in
          the name of the other Party, nor to bind the other Party to any other
          contract, agreement or undertaking with any Third Party.

    18.5  CORRESPONDENCE AND NOTICES.

          18.5.1    Correspondence, reports, documentation, and any other
                    communication in writing between the Parties in the course
                    of ordinary implementation of this Agreement shall be
                    delivered by hand, sent by facsimile, or by airmail to any
                    one employee appointed by the Party which is to receive such
                    written communication, or any other way as the Parties deem
                    appropriate.

          18.5.2    Extraordinary notices and communications (including but not
                    limited to notices of termination, force majeure, material
                    breach, change of address) shall be in writing and sent by
                    prepaid registered or certified air mail, or by facsimile
                    confirmed by prepaid registered or certified air mail
                    letter, and shall be deemed to have been properly served to
                    the addressee upon receipt of such written communication.

          18.5.3    In the case of CoCensys, the proper address for
                    communications and for all payments shall be:

                    CoCensys, Inc.
                    213 Technology Drive
                    Irvine, California 92618, USA
                    Attn:  Chief Executive Officer

                    and in the case of Wyeth-Ayerst, the proper address for
                    communications and for all payments shall be:

                    Wyeth-Ayerst Laboratories
                    555 Lancaster Avenue
                    St. Davids, PA  19087
                    Attn:  Senior Vice President, Global Business Development

          With a copy to:


                                      26.
<PAGE>

                    American Home Products Corporation
                    5 Giralda Farms
                    Madison, NJ  07940
                    Attn:  Senior Vice President and General Counsel

    18.6   CHOICE OF LAW.  This Agreement is subject to and governed by the
           laws of the State of Delaware, excluding its conflict of laws
           provisions.

    18.7   COUNTERPARTS.  This Agreement may be executed in one or more
           counterparts, each of which shall be an original and all of which
           shall constitute together the same document.

    18.8   APPOINTMENT OF WYETH-AYERST INTERNATIONAL, INC.  Wyeth-Ayerst hereby
           appoints Wyeth-Ayerst International Inc., a subsidiary company of
           Wyeth-Ayerst, organized and existing under the laws of the State of
           New York, U.S.A., having an office and place of business at 150
           Radnor-Chester Road, St. Davids Center, St. Davids, Pennsylvania
           19087, U.S.A., to administer as agent for Wyeth-Ayerst all the rights
           and obligations of Wyeth-Ayerst in respect of this Agreement,
           including, without limitation, the accounting of all royalties and
           other sums or payments due CoCensys hereunder, and the transmittal
           and receipt of all notices, reports, statements or other records
           relating to such royalties and the manufacture and sale of the
           Product. By its execution hereinbelow, Wyeth-Ayerst International
           Inc. accepts the designation and appointment set forth hereinabove.

This Agreement together with its Exhibits and further agreements mentioned
herein and Agreement No. 1 constitutes the entire agreement of the Parties with
respect to the subject matter hereof as of its date, and supersedes all prior
agreements, understandings, representations and proposals, written or oral,
relating thereto.

AMERICAN HOME PRODUCTS CORPORATION             COCENSYS, INC.



----------------------------------             ---------------------------------
Name                                           Name
Title                                          Title            


WYETH-AYERST INTERNATIONAL, INC.


----------------------------------
Name
Title     


                                     27.

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                                    EXHIBIT A
                                 
                       BACK-UP COMPOUND CANDIDATE CRITERIA


                Criterion for IND-Tracking     Activities Required
                --------------------------     -------------------

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                                   EXHIBIT B
                                 
                                 
                                 
                            [          *          ]
                                 

















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                                   EXHIBIT C
                                 
                            COCENSYS PATENT RIGHTS
                                 
                                 
                                 
 US   ISSUE DATE     EXPIRATION DATE     CORRESPONDING FOREIGN APPLICATIONS
------------------------------------------------------------------------------


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                                   EXHIBIT D
                                 
                                 
                       DEFINITION OF FULLY BURDENED COST
                                 

The following expenses are manufacturing expenses which are prepared in
accordance with generally accepted accounting principles consistently applied.

THE FOLLOWING EXPENSES ARE INCLUDED IN MANUFACTURING COSTS:


                           [          *          ]
      

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                                 EXHIBIT E
                                 
                         WYETH-AYERST PATENT RIGHTS
                                 
                                 
                                 
                                 
                                 
                           [          *          ]

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