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EXHIBIT 10.54

               INSTRUMENT, ASSAY DEVELOPMENT AND LICENSE AGREEMENT

                                     BETWEEN

                                  WYETH-AYERST

                                       AND

                         AURORA BIOSCIENCES CORPORATION




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This Agreement is made by and between AMERICAN HOME PRODUCTS, acting through its
WYETH-AYERST LABORATORIES DIVISION ("Wyeth"), a Delaware corporation with
principal offices at P.O. Box 8299, Philadelphia, PA 19101 and AURORA
BIOSCIENCES CORPORATION ("Aurora"), a Delaware corporation with principal
offices at 11010 Torreyana Road, San Diego, California 92121.

                                    RECITALS

WHEREAS, Wyeth and Aurora wish to enter into an agreement involving the purcase
by Wyeth of a Voltage-Ion Probe Reader (VIPR) from Aurora, collaborative
research to develop *** assays, and licenses of rights from Aurora to Wyeth to
use the VIPR as well as Aurora's Voltage Sensor Probes (VSPs) and *** assays to
practice the technologies and the assays as set forth herein.

Now, therefore, in consideration of the foregoing and the covenants and premises
contained herein the parties agree as follows:

1. DEFINITIONS

         1.1 "AURORA PATENTS" means U.S. patent *** and patent applications ***0
         and *** set forth in Exhibit A and ***s and ***, *** with respect
         thereto and *** patents issuing therefrom.

         1.2 "AURORA TECHNOLOGY" *** the Collaborative Research Program.

         1.3 "COLLABORATIVE RESEARCH PROGRAM" means the collaboration between
         Aurora and Wyeth as set forth in Exhibit B for the development of ***
         which may be amended from time to time, by written agreement of the
         parties.


         1.4 "CONFIDENTIAL INFORMATION" means all information, data, and
         documentation received by either party from the other party pursuant to
         this Agreement and if in writing, designated as confidential at the
         time of disclosure, subject to the exceptions set forth in Section 9.1.


         1.5 "CONTROL" or "CONTROLLED" means, in the context of intellectual
         property, possession by a party of the ability to grant a license or
         sublicense in accordance with the terms of this Agreement, and without
         violating the terms of any agreement by such party with any Third
         Party.


         1.6 "EFFECTIVE DATE" means the latest date on which the Agreement is
         executed by a party hereto.


         1.7 "INVENTION" means any new and useful process, machine, manufacture,
         or composition of matter, or improvement thereto, whether or not
         patentable.

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         1.8 "KNOW-HOW" means information and data owned or Controlled by a
         party hereto, which is existing as of the Effective Date or which a
         party develops or acquires as part of the Collaborative Research
         Program which is not generally known to the public, comprising:
         designs, concepts, algorithms, formulae, techniques, practices,
         processes, methods, knowledge, skill, experience, expertise and
         technical information.

         1.9 "MATERIALS" means any reagents, cell lines, promoters, enhancers,
         vectors, plasmids, genes, proteins and fragments thereof, peptides,
         antigens, antibodies, agonists, antagonists, inhibitors and chemicals.

         1.10 "TRACKING RECORD" means tracking records referred to in
         Section 5(e).

         1.11 "PATENT RIGHTS" means all U.S. or foreign (including regional
         authorities such as the European Patent Office) regular or provisional
         patent applications, including any continuation, continuation-in-part,
         or division thereof or any substitute application therefor or
         equivalent thereof, and any patent issuing thereon, including any
         reissue, reexamination or extension thereof and any confirmation patent
         or registration patent or patent of additions based on any such patent,
         containing one or more claims to an Invention (and in the case of an
         issued patent, containing one or more claims), and for which a party
         hereto owns or Controls, individually or jointly, any title thereto or
         rights thereunder.

         1.12 "REAGENT AGREEMENT" ***.

         1.12 "TECHNOLOGY" means Materials and Know-How.

         1.13 "THIRD PARTY" means any person or entity other than Aurora and
         Wyeth.

         1.14 "VIPR" means Aurora's voltage-ion probe reader for use with VSP's
         and purchased by Wyeth ***.

         1.15 "VOLTAGE SENSOR PROBES OR VSPS" means *** Aurora Patents.

         1.16 "WYETH MATERIALS" means *** Collaborative Research Program.

2.       EQUIPMENT PURCHASE

Aurora *** VIPR *** pursuant to this Agreement. Subject to Wyeth's payments in
Section 5, Aurora will provide the following:

         - Ship *** VIPR *** or within *** of the Effective Date, ***.

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         - *** VIPR at Wyeth's facility ***) days of shipment, *** expense.

         - Comprehensive *** VIPR for up to *** San Diego site to be scheduled
           approximately one week before the ***, with *** to be ***.

         - Warranty of the VIPR for *** after the Effective *** Section 5 (a).

3.       COLLABORATIVE RESEARCH

Aurora will develop, in collaboration with Wyeth, ***, and *** for the *** (as
defined in the the "Collaborative Research Program"), and will *** of
representative *** and other Technology to Wyeth as described herein.

Wyeth will provide pursuant to this Agreement the following Wyeth Materials and
Confidential Information to Aurora within *** days of the Effective Date:

         - *** which ***.

         - *** data documenting ***.

         - *** for the *** for *** into Aurora- ***, if the *** responses ***
           (see Section 5.b).

         - Up to ***.

         - Up to *** determine *** in a *** format.

Aurora will perform pursuant to this Agreement the following:

         - ***l for development of the *** incorporating *** format on the ***
           within ***.

         - *** development of the *** so that it can be used to *** respect ***.

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         - ***, if necessary, to *** for *** development.

         - *** determine *** provided by Wyeth.

         - *** assays ***.

         - Make available *** with these assays *** for each *** for the first
           year, *** to be contracted for *** Wyeth and Aurora).

The Collaborative Research Program shall be managed by a joint steering
committee of a size and composition ***, with *** from both Wyeth and Aurora,
minimally to include key representatives of Wyeth's ***. Each party shall have
*** vote in the joint steering committee. The Joint Steering Committee shall be
chaired by a *** representative. The term of the Collaborative Research Program
is *** year from the Effective Date, except for *** as provided in Section 10
below.

4.       LICENSES

As of the Effective Date this Agreement, Aurora will grant to Wyeth licenses and
rights as follows:

         a) A *** under the *** and *** to *** Wyeth's ***, except *** Aurora
         *** b) and c) ***. Such license grant is *** the ***. The license, ***.

         b) A *** under the *** to *** developed by Aurora *** Research ***.
         Such license grant is ***. The license, ***.

         c) A *** under the *** and *** to *** to *** developed *** or ***, and
         ***

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         research, ***, the *** is for *** only. The *** may not *** on ***. The
         payments for this license are set forth in Section 5. Such license
         grant is ***.

         d) If the license in Section 4 (c) *** the license grant of Section 4
         (c) will *** as ***. Aurora agrees that it *** including *** and/or ***
         for any purpose other *** under this Agreement, and will not *** to any
         Third Party without ***.

         4.1 Aurora is *** and *** Wyeth that directly arise from ***.

         4.2 RETAINED RIGHTS AND LIMITATIONS. The licenses under this Section 4
         are subject to Wyeth's obligations described herein including payments
         by Wyeth as set forth in Section 5. For clarity, the license rights
         granted to Wyeth in this Section 4 specifically exclude the right ***
         or ***; or 3) to *** or *** without the use of Wyeth Confidential
         Information or Wyeth Materials. As consideration for the rights
         received in Section 4, Wyeth *** Wyeth ***. ***.

5.       PAYMENTS

         a) EQUIPMENT PURCHASE. Wyeth *** Dollars ($***) for purchase ***.
         Shipping will be prepaid and added FOB San Diego to the invoice. The
         VIPR is provided ***, entitling Wyeth to *** of ***, prepaid and added
         ***. No one other than an Aurora factory certified engineer is
         authorized to service the VIPR, and any tampering with or modification
         of the instrument by any other party will nullify the warranty ***
         cause the license *** to terminate. *** approved by Aurora, in writing,
         which may include such

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         repairs described in training ("Authorized Maintenance"). ***.

         b) COLLABORATIVE RESEARCH. Wyeth will pay Aurora a *** fee of ***
         Dollars ($***) for the development of ***. This amount is payable in
         *** of *** Dollars ($***) each, the *** and the *** upon *** to Wyeth.
         In the event that the *** ***, as reasonably determined by Aurora,
         Aurora will notify the Joint Steering Committee. If the Joint Steering
         Committee agrees by *** as determined by Aurora, Aurora will notify the
         Joint Steering Committee, as soon as possible and prior to the date of
         *** from the Effective date. In the event, Wyeth is *** Aurora with ***
         from the Effective Date, (I) *** within *** of such ***; and (ii)
         Aurora shall ***. Aurora will provide reasonable telephone support for
         these assays as long as the license to them is maintained.

         c) LICENSE FEES. Wyeth *** license fee of *** Dollars ($***), *** on
         the anniversary of the Effective Date for *** years. After the initial
         ***, Wyeth may extend this license, ***, *** or *** for terms to be
         negotiated, in good faith, by the parties.

         d) ***. Upon designation by Wyeth *** on information *** with *** or
         *** above by virtue of such *** properties, Wyeth will pay Aurora ***.
         On the *** for each *** will pay *** of ***. On *** for each *** will
         pay *** Dollars ($***). ***. *** shall be due on *** by Wyeth as *** in
         a scientifically acceptable manner *** Wyeth, even if these ***
         subsequently *** VIPR or *** assays. *** the *** in either *** or
         unknown *** will be due.

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         e) PAYMENT AND TRACKING *** shall be paid within *** days after the end
         of each calendar quarter period in which *** are earned. The compounds,
         screens and targets tested using a screen developed under this
         Agreement will be recorded and stored by Wyeth using its customary
         means and in a computer searchable database on a storage device. The
         information stored *** upon in writing by the parties. Records of any
         *** subject to *** or *** by Wyeth in a *** or *** that may or may not
         *** related to the ***, or ***. Wyeth shall keep appropriate records of
         *** assays and *** including the VSPs ***. All the records described in
         this Section are collectively referred to as tracking records (the
         "Tracking Records"). Wyeth will *** Aurora and agreed to by Wyeth, and
         ***, to *** Tracking Records *** year upon reasonable prior *** Aurora
         for the *** the attainment of a milestone under this Section 5. The
         Tracking Records shall be securely retained according to Wyeth's ***
         than *** from *** VSPs. When a *** such as a *** or *** is *** safety
         or ***, Wyeth will *** Aurora under ***. On an annual basis, *** Aurora
         with a *** products that ***.

         f) ***. The parties acknowledge that the principal value contributed by
         Aurora under this Agreement is the ***, which the parties reasonably
         believe will lessen the time required to develop new products and to
         increase the efficiency of drug/target discovery and development
         processes and technologies. Wyeth acknowledges and agrees that the
         value it receives hereunder is in the access and use of ***;
         accordingly, Wyeth *** set forth herein. Additionally, the parties
         acknowledge that Aurora may not own or Control patent applications or
         patents covering the manufacture, sale, use or importation of a
         particular pharmaceutical product; provided, however, Wyeth ***
         pharmaceutical product or compound is *** Aurora Patents.

6.       OPTIONS

         a) LICENSE ***. As described in Section 4 (c), the *** *** Dollars
         ($***) plus

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         milestones ***. The license ***. ***, the license *** basis or for a
         *** negotiated in good faith by the parties.

         b) EXTENDED WARRANTY FOR THE VIPR. Aurora will provide an extended
         warranty package *** to Wyeth that includes *** and ***, prepaid and
         added to the service invoice ***. The price for *** Dollars ($***)***,
         increased annually by the Consumer Price Index (CPI), *** warranty
         within *** of the Effective Date; ***.

         c) SCIENTIFIC SUPPORT SERVICES. Aurora will provide Wyeth the
         opportunity to utilize a full range of scientific support services on
         licensed assays post transfer as mutually agreed in writing by the
         parties. A customized program can be designed for additional long-term
         support at commercially available rates beyond the scope of this
         project should Wyeth desire the same.

         d) TRAINING. Aurora will provide on-site training of Wyeth personnel in
         the use of the VIPR. Training will be for a maximum of *** people in a
         *** training program. Documentation and workbooks will be provided.
         ***. The price for this training program is *** Dollars ($***)***
         conducted in the continental US if requested *** of the Effective Date.

7.       INTELLECTUAL PROPERTY OWNERSHIP

PRE-EXISTING INTELLECTUAL PROPERTY. This agreement does not affect the ownership
of Inventions, Technology and Patent Rights of either party which existed prior
to the Effective Date.

INTELLECTUAL PROPERTY CREATED UNDER THE COLLABORATIVE RESEARCH PROGRAM. ***
developed by *** during the Collaborative Research Program will be owned by ***,
with *** as ***. ***, at its sole discretion, shall be responsible for the
filing and prosecution of all applicable patents and the expenses thereof. ***.

INTELLECTUAL PROPERTY ***. Any Inventions, Technology and Patent Rights relating
to the activities or properties of *** or other ***, *** of the licenses granted
by Aurora under Section 4. *** will be responsible for the filing and
prosecution of all applicable patents and for the expenses thereof. Any
improvements, Know-How, Inventions, Technology and Patent Rights

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developed *** VIPR or VSPs or their use will *** to Sections ***. ***.

TRANSFER OF RIGHTS. All rights not expressly licensed or assigned by Aurora are
retained by Aurora and no implied licenses are conveyed herein or were conveyed
before the Effective Date. Except as otherwise expressly provided in this
Agreement, nothing in this Agreement is intended to convey or transfer ownership
by one party to the other of any rights, title or interest in any Confidential
Information, Technology, copyrights or Patent Rights owned or Controlled by a
party. Except as expressly provided for in this Agreement, nothing in this
Agreement shall be construed as a license or sublicense by one party to the
other of any rights in any Technology, copyrights, or Patent Rights owned or
Controlled by a party.

INVENTORSHIP AND ASSIGNMENT. Inventorship of patentable inventions shall be
determined by U.S. patent law. Wyeth and Aurora ***.

COPYRIGHTS. The parties agree to treat and handle, to the maximum extent
practical, any copyrights owned or Controlled by a party in the same manner as
Patent Rights owned or Controlled by such party.


8.       PRODUCT DEVELOPMENT, COMMERCIALIZATION AND DILIGENCE

Wyeth will *** and such development and commercialization ***.

*** the Effective Date, and will *** Wyeth within ***of the Effective Date. The
*** will be made available to Wyeth in accordance with the *** between *** as
indicated in Section 3.


9.       CONFIDENTIALITY

     9.1 CONFIDENTIAL INFORMATION. Except as expressly provided herein, the
     parties agree that, for the term of this Agreement and five (5) years
     thereafter, the receiving party shall keep completely confidential and
     shall not publish or otherwise disclose to another party and shall not use
     for any purpose other than to perform the purposes contemplated by this
     Agreement any Confidential Information furnished to it by the disclosing
     party hereto pursuant to this Agreement, except that to the extent that it
     can be established by the receiving party by competent proof that such
     Confidential Information:

               was already known to the receiving party, other than under an
               obligation of confidentiality, at the time of disclosure;

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               was generally available to the public or otherwise part of the
               public domain at the time of its disclosure to the receiving
               party;
               became generally available to the public or otherwise part
               of the public domain after its disclosure and other than
               through any act or omission of the receiving party in breach
               of this Agreement;
               was lawfully disclosed to the receiving party by a person
               other than a party hereto,
               or was independently developed by the receiving party
               without the use of Confidential Information.

     9.2. PERMITTED USE AND DISCLOSURES. Each party hereto may use or disclose
     Confidential Information disclosed to it by the other party to the extent
     such use or disclosure is (i) reasonably necessary in filing or prosecuting
     patent applications, prosecuting or defending litigation, (ii) complying
     with applicable law, governmental regulation or court order, (iii)
     submitting information to tax or other governmental authorities, (iv)
     making a permitted sublicense or (v) otherwise exercising its rights
     hereunder, provided that if a party is required to make any such disclosure
     of another party's Confidential Information, other than pursuant to
     subsection (ii) hereof, it will give reasonable advance notice to the
     latter party of such disclosure and, shall obtain the prior written
     approval of said latter party, which approval shall not be unreasonably
     withheld.

     9.3 CONFIDENTIAL TERMS. Except as expressly provided herein, each party
     agrees not to disclose any material or financial terms of this Agreement to
     another party without the consent of the other party, not to be
     unreasonably withheld; provided, however, each party reserves the right to
     make reasonable disclosures (including the redaction of material or
     financial terms) as required by securities or other applicable laws, or to
     actual or prospective investors or corporate partners (including licensees
     and acquirers), or to accountants, attorneys and other professional
     advisors on a need-to-know basis under circumstances that reasonably ensure
     the confidentiality thereof, or to the extent required by law. If such
     Confidential Information is to become public information by such disclosure
     the disclosing party must obtain the written consent of the non-disclosing
     party in order to obtain protection of the Confidential Information if
     necessary.

     9.4 PRESS RELEASE. Notwithstanding the foregoing, the parties agree that
     Aurora will make a press release to announce the execution of this
     Agreement which shall be subject to prior written approval of Wyeth, such
     approval not to be unreasonably withheld. Thereafter, Wyeth and Aurora may
     each disclose to Third Parties the information contained in the mutually
     agreed upon press release without the need for further approval by the
     other.

10.      TERM AND TERMINATION OF THE RESEARCH COLLABORATION

         a) TERM. The Collaborative Research Program will terminate *** Wyeth,
         or after ***, unless extended by mutual written agreement of both
         parties through the Joint

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         Steering Committee. If the Collaborative Research Program *** Wyeth's
         ***, Wyeth will *** payment of *** Dollars ($***) described in Section
         *** above. In this case, the license described under Section *** and
         *** would *** Wyeth would *** for *** and to *** these assays under the
         terms of *** and pursuant to this Agreement, with *** or *** to Aurora,
         *** the VSPs, in which case it *** described in Section *** and ***.

         b) TERMINATION. Either party shall have the right to terminate this
         Agreement at any time during the term for a material breach of this
         Agreement by the other party, provided that the non-breaching party
         shall have first given *** days prior written notice (*** days in the
         event of non-payment of any amounts due under this Agreement) to the
         breaching party describing such breach and stating the non-breaching
         party's intention to terminate this Agreement if such breach remains
         uncured, and the breaching party thereafter fails to cure same within
         such *** day (***) period (*** day period in the event of non-payment
         of any amounts due under this Agreement).

         c) EFFECT OF EXPIRATION OR TERMINATION. Except as otherwise expressly
         provided in this Agreement, the rights and obligations of the parties
         hereof shall terminate and be of no further force or effect whatsoever
         upon any termination of this Agreement under Section 10 hereof.
         Sections *** shall survive termination or expiration of this Agreement.
         Upon expiration or other termination of the Agreement all licenses
         granted will thereby terminate and Materials will be destroyed or
         returned at the direction of the parties within *** days.

11.      MISCELLANEOUS

     11.1.BINDING EFFECT; ASSIGNMENT. This Agreement shall be binding upon the
     parties' permitted successors and permitted assigns. Wyeth may not assign
     or otherwise transfer this Agreement or any of its rights or obligations
     hereunder without the prior written consent of Aurora *** such attempted
     assignment or transfer shall be void. Aurora may assign or otherwise
     transfer this Agreement without the consent of Wyeth.

     11.2. EFFECT OF WAIVER. No waiver of any default, condition, provisions or
     breach of this Agreement shall be deemed to imply or constitute a waiver of
     any other like default, condition, provision or breach of this Agreement.

     11.3. REPRESENTATIONS AND WARRANTIES OF AURORA AND WYETH. Each Party hereby
     represents and warrants: Such party is duly organized and validly existing
     and in good standing under the laws of the state of its incorporation and
     has all requisite corporate power and authority to enter into this
     Agreement and to carry out the provisions hereof. Such party is duly
     authorized to execute and deliver this Agreement and to perform its
     obligations hereunder. This Agreement is a legal and valid obligation
     binding upon it and enforceable in accordance

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     with its terms. The execution, delivery and performance of this Agreement
     by such party does not conflict with any agreement, instrument or
     understanding, oral or written, to which it is a party or by which it may
     be bound, nor violate any law or regulation of any court, governmental body
     or administrative or other agency having jurisdiction over it.

         11.3.1 Aurora hereby represents and warrants to Wyeth that, to the best
         of its knowledge:

              (a) ***
              (b) as of the Effective Date, it has the full right, power and
              authority to grant the licenses granted to Wyeth hereunder;
              (c) ***;
              (d) it is the exclusive licensee of the Aurora Patents and Aurora
              Technology existing as of the Effective Date, ***.
              (e) ***

     11.4. ***

         11.4.1. ***

         11.4.2. ***

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         11.4.3.  ***

     11.5. FORCE MAJEURE. Neither party shall lose any rights hereunder or be
     liable to the other party for damages or losses (except for payment
     obligations) on account of failure of performance by the defaulting party
     if the failure is occasioned by war, strike, fire, act of God(s),
     earthquake, flood (including El Nino and La Nina), lockout, embargo and
     governmental acts or orders or restrictions.

     11.6. AMENDMENT. No modification, supplement to or waiver of this Agreement
     or any Addendum hereto or any of their provisions shall be binding upon a
     party hereto unless made in writing and duly signed by an authorized
     representative of both Wyeth and Aurora. In no event may the terms of this
     Agreement be changed, deleted, supplemented or waived by any notice,
     purchase order, receipt, acceptance, bill of lading or other similar form
     of document. A failure of either party to exercise any right or remedy
     hereunder, in whole or in part, or on one or more occasions, shall not be
     deemed either a waiver of such right or remedy to the extent not exercised,
     or of any other right or remedy, on such occasion, or a waiver of any right
     or remedy on any succeeding occasion.

     11.7. ENTIRE AGREEMENT. This Agreement and each supplemental written
     agreement contemplated hereunder, sets forth the entire understanding and
     agreement of the parties as to the subject matter thereof, and there are no
     other understandings, representations or promises, written or verbal, not
     set forth herein or on which either party has relied. If any provisions of
     any such Addendum or supplemental written agreement conflict with any
     provisions set forth in this Agreement, the provisions of this Agreement
     shall take precedence, unless such Addendum or supplemental written
     agreement expressly refers to the specific provision(s) of this Agreement
     that it is intended to replace or modify (and which shall be limited in
     force and effect to such Addendum or supplemental written agreement only).

     11.8. NOTICES. All Notices under this Agreement shall be given in writing
     and shall be addressed to the parties at the following addresses:

                           FOR WYETH:

                                    Wyeth-Ayerst Laboratories
                                    P.O. Box 8299
                                    Philadelphia, PA 19101
                           Attn: SVP, Global Business Development

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                           Copy to: American Home Products Corporation
                                    5 Giralda Farms
                                    Madison, NJ 07940
                                    Attn: SVP and General Counsel

                           FOR AURORA:

                                    Timothy J. Rink, M.D., D.Sc.
                                    CEO and Chairman
                                    Aurora Biosciences Corporation
                                    11010 Torreyana Road
                                    San Diego, CA.  92121

                                    COPIES TO:
                                    John D. Mendlein, Ph.D., J.D.
                                    Senior Vice President, Intellectual Property
                                    and Chief Knowledge Officer
                                    Aurora Biosciences Corporation
                                    11010 Torreyana Road
                                    San Diego, CA.  92121

     Notices shall be in writing and shall be deemed delivered when received, if
     delivered by a courier, or on the second business day following mailing, if
     sent by first-class certified or registered mail, postage prepaid.

     11.9. RESOLUTION. The parties recognize that disputes as to certain matters
     may from time to time arise during the term of this Agreement which relate
     to either party's rights and/or obligations hereunder. It is the objective
     of the parties to establish procedures to facilitate the resolution of
     disputes arising under this Agreement in an expedient manner by mutual
     cooperation and without resort to resolution by other means. The parties
     agree that prior to any resolution concerning this Agreement, *** will meet
     in person or by video-conferencing in a good faith effort to resolve any
     disputes concerning this Agreement. Within *** days of a formal request by
     either party to the other, any party may, by written notice to the other,
     have such dispute referred to their respective officers designated or their
     successors, for attempted resolution by good faith negotiations, such good
     faith negotiations to begin within *** after such notice is ***.

     11.10. GOVERNING LAW. This Agreement shall be governed by and construed in
     accordance with the laws ***, without regard or giving effect to its
     principles of conflict of laws.

     11.11. THIRD PARTY BENEFICIARIES. This Agreement and the rights and
     obligations created hereunder are for the sole benefit of the parties
     hereto and their respective successors or assigns as may be permitted under
     the terms of this Agreement. By entering into this Agreement, the parties
     agree that they are not creating and do not intend to create implied or
     incidental rights inuring to the benefit of Third Parties.

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     11.12. SEVERABILITY. This Agreement is intended to be severable. If any
     provision(s) of this Agreement are or become invalid, are ruled illegal by
     a court of competent jurisdiction or are deemed unenforceable under the
     current applicable law from time to time in effect during the term hereof,
     it is the intention of the parties that the remainder of the Agreement
     shall not be affected thereby and shall continue to be construed to the
     maximum extent permitted by law at such time. It is further the intention
     of the parties that in lieu of each such provision which is invalid,
     illegal, or unenforceable, there shall be substituted or added as part of
     this Agreement by such court of competent jurisdiction a provision which
     shall be as similar as possible, in economic and business objectives as
     intended by the parties to such invalid, illegal or unenforceable
     provision, but shall be valid, legal and enforceable.

     11.13. HEADINGS. Captions and paragraph headings are for convenience only
     and shall not form an interpretative part of this Agreement. Unless
     otherwise specifically provided, all references to a Section incorporate
     all Sections or subsections thereunder. This Agreement shall not be
     strictly construed against either party hereto and maybe executed in two
     (2) or more counterparts, each of which will be deemed an original and the
     same instrument. Counterparts may be signed and delivered by facsimile,
     each of which shall be binding when sent, and in each case an original
     shall be sent via overnight courier. This Agreement will not be enforceable
     and shall have no effect if this Agreement is not executed by Wyeth and
     Aurora ***.

     IN WITNESS WHEREOF, the parties have executed, by duly authorized
representatives, this Agreement:

By: /s/ Egan E. Berg                         By: /s/ Michael J. Dunn
   ----------------------------                 ------------------------------
Date: 12/16/99                               Date: November 18, 1999
     --------------------------                   ----------------------------
Name: Egan E. Berg                           Name: Michael J. Dunn
    ---------------------------                   ----------------------------
Title: Vice President                        Title: V.P. Business Development
     --------------------------                    ---------------------------
For American Home Products                   For Aurora Biosciences Corporation
Acting through its Wyeth-Ayerst
Laboratories Division


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                                    EXHIBIT A

                                 AURORA PATENTS

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                                    EXHIBIT B

                  DESCRIPTION OF COLLABORATIVE RESEARCH PROGRAM


                                     [GRAPHIC]


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                                    EXHIBIT C

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                                   EXHIBIT 1.1

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                                   EXHIBIT 1.2

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