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                                                                   EXHIBIT 99.8









                  RESEARCH COLLABORATION AND LICENSE AGREEMENT


                                 by and between


                        TEXAS BIOTECHNOLOGY CORPORATION

                                      and

                              SCHERING-PLOUGH LTD.

                                     dated

                                 June 30, 2000

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                              TABLE OF CONTENTS
                                                                        Page
I.       DEFINITIONS

         1.1      Additional Development Candidate........................2
         1.2      Affiliate...............................................2
         1.3      [*].....................................................2
         1.4      [*].....................................................2
         1.5      [*].....................................................2
         1.6      [*].....................................................2
         1.7      Calendar Quarter........................................2
         1.8      Calendar Year...........................................2
         1.9      Combination Product.....................................2
         1.10     Development Candidate...................................3
         1.11     Field...................................................3
         1.12     First Commercial Sale...................................3
         1.13     FTE.....................................................3
         1.14     Good Laboratory Practices...............................3
         1.15     HRD.....................................................3
         1.16     Improvement.............................................3
         1.17     IND.....................................................3
         1.18     Joint Invention.........................................4
         1.19     Licensed Compound(s)....................................4
         1.20     Licensed Products(s)....................................4
         1.21     Material(s).............................................4
         1.22     NDA.....................................................4
         1.23     Net Sales...............................................4
         1.24     [*].....................................................4
         1.25     Proprietary Information.................................4
         1.26     Regulatory Approval.....................................4
         1.27     Research Committee......................................5
         1.28     Research Inventions.....................................5
         1.29     Research Plan...........................................5
         1.30     Research Program........................................5
         1.31     Research Term...........................................5
         1.32     SP Ltd. Know-How........................................5
         1.33     TBC Invention...........................................6
         1.34     Territory...............................................6
         1.35     U.S. Agreement..........................................6
         1.36     Valid Claim.............................................6
         1.37     VLA-4...................................................6
         1.38     VLA-4 Compound..........................................6
         1.39     VLA-4 Know-How..........................................6
         1.40     VLA-4 Patent Rights.....................................7

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II.      RESEARCH PROGRAM

         2.1      General.................................................7
         2.2      Performance of Research Program.........................7
         2.3      [*].....................................................8
         2.4      Know-How Disclosures....................................8
         2.5      Records and Reports.....................................8
         2.6      Research Invention......................................8
         2.7      License of Research Inventions..........................9
         2.8      Research Term...........................................9
         2.9      Termination of Research Program.........................9

III.     LICENSE

         3.1      License.................................................9
         3.2      Right to Sublicense.....................................9
         3.3      License to TBC..........................................10
         3.4      [*].....................................................10
         3.5      [*].....................................................10

IV.      DEVELOPMENT AND COMMERCIALIZATION

         4.1      [*].....................................................10
         4.2      [*].....................................................10
         4.3      [*].....................................................10
         4.4      [*].....................................................10
         4.5      [*].....................................................10
         4.6      [*].....................................................10
         4.7      [*].....................................................10

V.       PAYMENTS; ROYALTIES AND REPORTS

         5.1      Additional Payment Obligations..........................10
         5.2      Research Program Funding................................11
         5.3      Consideration for License...............................11
         5.4      Milestone Payments......................................11
         5.5      [*].....................................................11
         5.6      Royalties...............................................11
5.7      Reports; Payment of Royalty; Payment Exchange Rate and
                          and Currency Conversions........................12
         5.8      Maintenance of Records; Audits..........................12
         5.9      Income Tax Withholding..................................12
         5.10     Direct Affiliate Licenses...............................12
         5.11     Animal Health Indications...............................13


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VI.      PATENTS

         6.1      Filing; Prosecution and Maintenance of Patents..........13
         6.2      [*].....................................................13
         6.3      Enforcement.............................................13
         6.4      Infringement and Third Party Licenses...................13
         6.5      Third Party Infringement Suit...........................13
         6.6      Abandonment.............................................13
         6.7      Patent Term Restoration.................................13
         6.8      Notices Regarding Patents...............................13

VII.     CONFIDENTIALITY AND PUBLICATION

         7.1      Confidentiality.........................................14
         7.2      Return of Confidential Information......................15
         7.3      No Publicity............................................16
         7.4      Publication.............................................16

VIII.    REPRESENTATIONS AND WARRANTIES

         8.1      Representations and Warranties of Each Party............16
         8.2      TBC's Representations...................................17
         8.3      SP Ltd.'s Representations...............................18
         8.4      No Inconsistent Agreements..............................19
         8.5      Representation by Legal Counsel.........................19

IX.      INDEMNIFICATION AND LIMITATION ON LIABILITY

         9.1      Indemnification by SP Ltd...............................19
         9.2      Indemnification by TBC..................................20
         9.3      Conditions to Indemnification...........................20
         9.4      Settlements.............................................20
         9.5      Limitation of Liability.................................21
         9.6      Insurance...............................................21

X.       TERM AND TERMINATION

         10.1     Term and Expiration.....................................21
         10.2     Termination by SP Ltd...................................21
         10.3     Termination.............................................21
         10.4     Effect of Termination...................................22
         10.5     [*].....................................................22


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XI.      MISCELLANEOUS

         11.1     Assignment/Change of Control............................22
         11.2     Governing Law...........................................23
         11.3     Waiver..................................................23
         11.4     Independent Relationship................................23
         11.5     Export Control..........................................23
         11.6     Entire Agreement; Amendment.............................23
         11.7     Notices.................................................24
         11.8     Provisions for Insolvency...............................25
         11.9     Force Majeure...........................................26
         11.10    Severability............................................27
         11.11    Counterparts............................................27
         11.12    Captions................................................27
         11.13    Recording...............................................27
         11.14    Relationship to U.S. Agreement, Controlling Provisions..27
         11.15    Further Actions.........................................28

         SCHEDULES

         1.10     Development Criteria
         1.23     Schedule of Fully Allocated Manufacturing Costs
         1.29     Research Plan
         1.40     VLA-4 Patent Rights
         5.7      Policy of Bookkeeping Exchange Rates
         11.2     [*]


[*] designates portions of this document that have been omitted pursuant to a
request for confidential treatment filed with the Commission.


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                  RESEARCH COLLABORATION AND LICENSE AGREEMENT

         THIS RESEARCH COLLABORATION AND LICENSE AGREEMENT (the "Agreement") is
made effective as of June 30, 2000 (the "Effective Date"), by and between TEXAS
BIOTECHNOLOGY CORPORATION., a corporation organized and existing under the laws
of Delaware and having its principal place of business at 7000 Fannin, Houston,
TX 77030 (hereinafter referred to as "TBC") and SCHERING-PLOUGH LTD., a
corporation organized and existing under the laws of Switzerland and having its
principal place of business at Toepferstrasse 5, 6004 Lucerne, Switzerland,
(hereinafter referred to as "SP Ltd."). TBC and SP Ltd. are sometimes referred
to herein individually as a party and collectively as the parties. References
to "SP Ltd." and "TBC" shall include their respective Affiliates (as
hereinafter defined).

         WHEREAS TBC has developed certain VLA-4 Know-How and Materials
relating to VLA-4 Compounds (each as hereinafter defined); and

         WHEREAS TBC desires to initiate a program to optimize and commercially
develop such VLA-4 Compounds; and

         WHEREAS SP Ltd. desires to enter into a research program to identify,
optimize and commercially develop VLA-4 Compounds; and

         WHEREAS SP Ltd. and TBC desire to enter into a research collaboration
to discover and develop Licensed Product(s) (as hereinafter defined) upon the
terms and conditions set forth herein; and

         WHEREAS SP Ltd. desires to obtain, and TBC is willing to grant to SP
Ltd., a license under the VLA-4 Patent Rights and to use the VLA-4 Know-How,
upon the terms and conditions set forth herein; and

         WHEREAS TBC and Schering Corporation, an Affiliate of SP Ltd.
(hereinafter referred to as "Schering") have entered into a contemporaneous
Research Collaboration and License Agreement relating to the United States and
its territories, possessions and commonwealths (the "U.S. Agreement").

         NOW, THEREFORE, in consideration of the foregoing premises and the
mutual covenants herein contained, SP Ltd. and TBC hereby agree as follows:

<PAGE>   7

ARTICLE I - DEFINITIONS

         As used in this Agreement, the following capitalized terms, whether
used in the singular or plural, shall have the respective meanings set forth
below:

1.1 "Additional Development Candidate" shall have the meaning set
forth in Section 2.9

1.2 "Affiliate" shall mean any individual or entity directly or indirectly
controlling, controlled by or under common control with, a party to this
Agreement. For purposes of this Agreement, the direct or indirect ownership of
fifty percent (50%) or more of the outstanding voting securities of an entity,
or the right to receive fifty percent (50%) or more of the profits or earnings
of an entity shall be deemed to constitute control. Such other relationship as
in fact results in actual control over the management, business and affairs of
an entity shall also be deemed to constitute control.

1.3   [*]

1.4   [*]

1.5   [*]

1.6   [*]

1.7 "Calendar Quarter" shall mean the respective periods of three (3)
consecutive calendar months ending on March 31, June 30, September 30 and
December 31, for so long as this Agreement is in effect.

1.8 "Calendar Year" shall mean each successive period of twelve (12) months
commencing on January 1 and ending on December 31, for so long as this
Agreement is in effect.

1.9 "Combination Product" shall mean a Licensed Product which comprises two (2)
or more active ingredients at least one (1) of which is a Licensed Compound
covered by a Valid Claim.

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[*] Designates portions of this document that have been omitted pursuant to
    a request for confidential treatment filed with the Commission.


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1.10 "Development Candidate" shall mean any VLA-4 Compound which meets the
criteria for development set forth in Schedule 1.10 or such other criteria [*].

1.11 "Field" shall mean the use of VLA-4 Compounds to treat or prevent any
disease, disorder or condition in humans or animals.

1.12 "First Commercial Sale" shall mean, with respect to any Licensed Product,
the first sale for end use of such Licensed Product in a country in the
Territory after receipt of the requisite Regulatory Approval.

1.13 "FTE" shall mean an effort substantially equivalent to one (1) full-time
research personnel dedicated for a period of one year, based, in general, on an
eight-hour workday and a 48-week working year.

1.14 "Good Laboratory Practices" shall mean the standards and practices
recommended by the International Conference on Harmonisation (as varied from
time to time) regulating the non-human testing of pharmaceutical products.

1.15 "HRD" shall mean a health registration dossier or its equivalent covering a
Licensed Product filed in any country in the Territory and which is analogous to
an NDA and including, where applicable, applications for pricing, pricing
reimbursement approval, labeling and Regulatory Approval.

1.16 "Improvement" shall mean any enhancement in the manufacture, formulation,
ingredients, preparation, presentation, means of delivery, dosage, or packaging
of, or any new therapeutic indications for, Licensed Product.

1.17 "IND" shall mean an investigational new drug application or its equivalent
filed with the United States Food and Drug Administration for beginning
clinical trials in humans, or any comparable application filed with the
regulatory authorities of a country other than the United States prior to
beginning clinical trials in humans in that country, with respect to Licensed
Product(s).

1.18 "Joint Invention" shall have the meaning set forth in Section 2.6.

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[*] Designates portions of this document that have been omitted pursuant to
    a request for confidential treatment filed with the Commission.


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1.19     "Licensed Compound(s)" shall mean any VLA-4 Compound [*].

1.20 "Licensed Product(s)" shall mean any form or dosage of pharmaceutical
compositions or preparations, including, without limitation, Combination
Products, in final form for sale by prescription, over-the-counter or any other
method, which contain as an active ingredient one or more Licensed Compounds.

1.21 "Material(s)" shall mean any chemical or biological materials, other than
Licensed Compound(s) and Licensed Product(s), relating (i) to VLA-4 or VLA-4
Compounds, and (ii) upon the Option Date, [*], and in each case which are
discovered and/or developed by or on behalf of TBC and/or any of its Affiliates
prior to the Effective Date or the Option Date, as the case may be, or by or on
behalf of TBC and/or any of its Affiliates during the Research Term and in
performance of the Research Program.

1.22 "NDA" shall mean a New Drug Application, Product License Application or
its equivalent filed with the United States Food and Drug Administration
seeking approval to market and sell a Licensed Product in the United States.

1.23 "Net Sales" shall mean, with respect to each country in the Territory,
amounts actually received on sales by SP Ltd., its Affiliates or sublicensees
on all sales of Licensed Product to an unaffiliated third party (whether an
end-user, a distributor or otherwise) [*].

1.24     [*]

1.25 "Proprietary Information" shall mean, as applicable, all SP Ltd. Know-How,
VLA-4 Know-How [*] and all other scientific, clinical, regulatory, marketing,
financial and commercial information or data, whether communicated in writing,
verbally or electronically, which is provided by one party to the other party
in connection with this Agreement.

1.26 "Regulatory Approval" shall mean any applications or approvals, including
any INDs, NDAs, HRDs, supplements, amendments, pre- and post-approvals,
marketing authorizations based upon such approvals (including any prerequisite
manufacturing approvals or authorizations related thereto) and pricing, third
party reimbursement or labeling approval(s), technical, medical

-----------------
[*] Designates portions of this document that have been omitted pursuant to
    a request for confidential treatment filed with the Commission.


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and scientific licenses, registrations or authorizations of any national,
supra-national (e.g. the European Commission, the Council of the European Union,
or the European Agency for the Evaluation of Medicinal Products), regional,
state or local regulatory agency, department, bureau, commission, council or
other governmental entity, necessary for the manufacture, distribution, use,
import, export or sale of Licensed Product(s) and/or Licensed Compound(s) in the
Territory.

1.27     [*]

1.28 "Research Inventions" shall have the meaning set forth in Section 2.6
hereof.

1.29 "Research Plan" shall mean the research plan which is attached hereto as
Schedule 1.29 and herein incorporated by reference, including as it may be
amended from time to time during the Research Term upon the mutual written
agreement of the parties.

1.30 "Research Program" means the research effort to identify and develop VLA-4
Compounds which is to be conducted by TBC as described in the Research Plan.

1.31 "Research Term" shall mean the Initial Research Term and the Extended
Research Term, if any, as set forth in Section 2.8 hereof.

1.32 "SP Ltd. Know-How" shall mean any information, know-how or materials: (i)
owned or controlled by SP Ltd. and/or any of its Affiliates as of the Effective
Date relating to VLA-4 Compounds or derivatives thereof; (ii) discovered or
developed by or on behalf of SP Ltd. and/or any of its Affiliates during the
term of this Agreement; or (iii) owned or controlled by SP Ltd. and/or any of
its Affiliates relating to the development, manufacture, marketing, use or sale
of Licensed Compound(s) and/or Licensed Product(s), and in each case which
during the term of this Agreement are not generally known. SP Ltd. Know-How
shall include, without limitation, all applications, registrations, licenses,
authorizations, approvals and correspondence related to Licensed Compound(s)
and/or Licensed Product(s) submitted by SP Ltd. to regulatory authorities as
well as all biological, chemical, pharmacological, toxicological,
pharmaceutical, physical and analytical, clinical, safety, manufacturing and
quality control data and information related thereto.

1.33     "TBC Invention" shall have the meaning set forth in Section 2.6.

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[*] Designates portions of this document that have been omitted pursuant to
    a request for confidential treatment filed with the Commission.


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1.34 "Territory" shall mean all of the countries and territories in the world,
excluding the United States and its territories, commonwealths and possessions.

1.35 "U.S. Agreement" shall have the meaning set forth in the sixth
recital hereof.

1.36 "Valid Claim" means a composition-of-matter or method-of-use claim of an
issued and unexpired patent included within the VLA-4 Patent Rights, which has
not been revoked or held unenforceable or invalid by a decision of a court or
other governmental agency of competent jurisdiction, unappealable or unappealed
within the time allowed for appeal, and which has not been disclaimed, denied
or admitted to be invalid or unenforceable through reissue or disclaimer or
otherwise.

1.37 "VLA-4" means the alpha-4-beta-1 integrin receptor subtype.

1.38 "VLA-4 Compound" shall mean [*].

1.39 "VLA-4 Know-How" shall mean any information, know-how or materials: (i)
owned or controlled by TBC and/or any of its Affiliates as of the Effective
Date relating to VLA-4; (ii) discovered or developed by or on behalf of TBC
and/or any of its Affiliates during the term of this Agreement in performance
of the Research Program; or (iii) owned or controlled by TBC and/or any of its
Affiliates relating to the research, development, manufacture, marketing, use
or sale of Licensed Compound(s) and/or Licensed Product(s), and in each case
which are not in the public domain. VLA-4 Know-How shall include, without
limitation, all applications, registrations, licenses, authorizations,
approvals and correspondence relating to Licensed Compound(s) and/or Licensed
Product(s) submitted by TBC to regulatory authorities as well as all
biological, chemical, pharmacological, toxicological, pharmaceutical, physical
and analytical, clinical, safety, manufacturing and quality control data and
information related thereto.

1.40 "VLA-4 Patent Rights" shall mean any and all patents and patent
applications (which for the purposes of this Agreement shall be deemed to
include certificates of invention and applications for certificates of
invention) which during the term of this Agreement are owned by TBC (and/or any
of its Affiliates), or to which TBC (and/or any of its Affiliates) through
license or otherwise acquires rights, including, but not limited to, those
listed in Schedule 1.40, which

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[*] Designates portions of this document that have been omitted pursuant to
    a request for confidential treatment filed with the Commission.


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(A) have claims covering: (i) Material or methods for the preparation or use
thereof; (ii) VLA-4 Compound or the manufacture and/or use thereof, (iii)
Licensed Product containing a VLA-4 Compound or the manufacture and/or use
thereof, or (iv) subject matter which is or relates to Research Inventions; (B)
are substitutions, divisions, continuations, continuations-in-part, reissues,
renewals, registrations, confirmations, re-examinations, extensions,
supplementary protection certificates or the like, or the provisional
applications of any such patents and patent applications; or (C) are foreign
equivalents of any of the above.

                         ARTICLE II - RESEARCH PROGRAM

2.1 General TBC shall engage in the Research Program upon the terms and
conditions set forth in this Agreement, including any applicable Schedules or
Exhibits attached hereto. The activities to be undertaken in the course of
Research Program are set forth in the Research Plan.

2.2 Performance of Research Program

    (a) Conduct of Research TBC shall conduct the Research Program in good
scientific manner, and in compliance, in all material respects, with all
material requirements of applicable laws, rules and regulations and all
applicable Good Laboratory Practices to attempt to achieve its objectives
efficiently and expeditiously. TBC shall proceed diligently with the work
contemplated under this Agreement, including, without limitation, as set forth
in the Research Plan, by using good faith efforts to provide, among others, the
following resources:

         (i)      [*]; and.
         (ii)     [*].

                  While TBC agrees to proceed diligently with the work
contemplated under this Agreement, neither TBC nor SP Ltd. warrants or
guarantees that their efforts will result in a marketable or approvable
Development Candidate, Licensed Compound or Licensed Product, or that the goals
specified in the Research Plan will be achieved within the periods set forth
therein.

    (b) Research Effort During the Research Term, including as it may be
extended, TBC shall maintain its activities in performance of the Research
Program at a level appropriate for completion of the Research Program during
the Research Term. [*]

    (c)      Personnel  [*].

2.3      Research Committee
         (a)      [*]

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[*] Designates portions of this document that have been omitted pursuant to
    a request for confidential treatment filed with the Commission.


                                      -7-

<PAGE>   13
         (b)      [*]
         (c)      [*]
         (d)      [*]

2.4 Know-How Disclosures As soon as practicable after the Effective Date,
TBC shall disclose to SP Ltd. in writing all VLA-4 Know-How [*] not
previously disclosed to SP Ltd. During the term of the Research Program,
TBC shall also promptly disclose to SP Ltd. in writing on an ongoing basis
all VLA-4 Know-How as it is developed, and if requested in writing by
SP Ltd., copies of the records described in Section 2.5 [*].

2.5 Records and Reports

    (a) Record Keeping TBC shall maintain records, in sufficient detail
and in good scientific manner appropriate for patent and regulatory purposes,
which shall be complete and accurate in all material respects and shall fully
and properly reflect all work done and results achieved in the performance of
the Research Program. Such records shall include books, records, reports,
research notes, charts, graphs, comments, computations, analyses, recordings,
photographs, computer programs and documentation thereof, computer information
storage media, samples of materials and other graphic or written date generated
in connection with the Research Program, including any data required to be
maintained pursuant to all requirements of applicable laws, rules and
regulations.

    (b)      [*]

2.6 Research Inventions The entire right, title and interest in all
discoveries, Improvements, processes, formulas, data, inventions, know-how and
trade secrets, whether or not patentable, and any patent applications or
patents based thereon in the Territory, relating to Materials, Licensed
Compound(s) and/or Licensed Product(s) and which are made, conceived or reduced
to practice:

    (i) solely by employees or agents of TBC (or its Affiliate) shall be
owned solely by TBC ("TBC Inventions");


    (ii) solely by employees or agents of SP Ltd. (or its Affiliate) shall
be owned solely by SP Ltd. ("SP Ltd. Inventions"); and


    (iii) jointly by employees or agents of TBC and employees or agents of
SP Ltd. (or their respective Affiliates) shall be owned jointly by TBC and SP
Ltd. ("Joint Inventions"). TBC Inventions and Joint Inventions shall
hereinafter be referred to collectively as "Research Inventions".

2.7 License of Research Inventions

    (a)   [*]
    (b)   [*]

2.8 Research Term  The term of the Research Program shall commence on the
Effective Date [*].

-----------------
[*] Designates portions of this document that have been omitted pursuant to
    a request for confidential treatment filed with the Commission.


                                      -8-

<PAGE>   14

2.9 Termination of Research Program  [*]


                             ARTICLE III - LICENSE

3.1      License Grant

         (a) VLA-4 License Grant TBC hereby grants to SP Ltd. an exclusive
license in the Territory in the Field under the VLA-4 Patent Rights and to use
the VLA-4 Know-How to discover, develop, make, have made, import, export, use,
manufacture, have manufactured, distribute, market, promote, offer for sale and
sell Licensed Compound(s) and/or Licensed Product(s). TBC shall retain the
right to use the VLA-4 Patent Rights and VLA-4 Know-How [*].

         (b) VLA-4 Non-Exclusive License Grant In the event that the discovery,
development, making, having made, importing, exporting, use, manufacturing,
having manufactured, distribution, marketing, promotion, offering for sale or
sale by SP Ltd., its Affiliates and/or sublicensees of Licensed Compound(s)
and/or Licensed Product(s) would, during the term of this Agreement, infringe a
claim of an issued letters patent, or any other patent rights which TBC owns or
has the rights to license and which patents are not covered by the grant in
Section 3.1(a), TBC hereby grants to SP Ltd., to the extent TBC is legally able
to do so, a non-exclusive, [*] license in the Territory under such issued
letters patent solely for SP Ltd. to discover, develop, make, have made, import,
export, use, manufacture, have manufactured, distribute, market, promote, offer
for sale and sell Licensed Compound(s) and/or Licensed Product(s) in the
Territory. [*]

3.2      Right to Sublicense  [*]

3.3      License to TBC   [*]

3.4      [*]

3.5      Option to [*]
         (a) [*]
         (b) [*]
         (c) [*]

-----------------
[*] Designates portions of this document that have been omitted pursuant to
    a request for confidential treatment filed with the Commission.


                                      -9-

<PAGE>   15


                 ARTICLE IV - DEVELOPMENT AND COMMERCIALIZATION

4.1      [*]
         (a)      [*]
         (b)      [*]

4.2      [*]

4.3      Discontinuance of Development
         (a)      [*]
         (b)      [*]

4.4      [*]

4.5      [*]

4.6      [*]

4.7      [*]

                  ARTICLE V - PAYMENTS; ROYALTIES AND REPORTS

5.1 Additional Payment Obligations The parties acknowledge that SP Ltd.'s
payment obligations as set forth in Sections 5.2, 5.3, 5.4, 5.5 and 5.6 of this
Agreement are in addition to the payment obligations of Schering Corporation
set forth in Section 5.2, 5.3, 5.4, 5.5 and 5.6 of the U.S. Agreement.

5.2 Research Program Funding In consideration for TBC's performance of its
obligations under the Research Program, SP Ltd. shall pay to TBC research [*].

5.3 Consideration for License In consideration for the licenses granted to SP
Ltd. hereunder, SP Ltd. shall pay to TBC a license fee [*].

-----------------
[*] Designates portions of this document that have been omitted pursuant to
    a request for confidential treatment filed with the Commission.


                                     -10-

<PAGE>   16

5.4 Milestone Payments Subject to the terms and conditions of this Agreement
and in consideration for the ongoing provision of data, information and
know-how, SP Ltd. shall pay to TBC the following payments based on attainment
of the research and development milestones indicated:

                  [*]

SP Ltd. shall notify TBC in writing within thirty (30) calendar days upon the
achievement of each milestone, such notice to be accompanied by payment of the
appropriate milestone payment. The applicable milestone payment shall be
payable only upon the initial achievement of such milestone and no amounts
shall be due hereunder for subsequent or repeated achievement of such
milestone.

5.5      [*]

5.6 Royalties

    (a) Royalty Rates Subject to the terms and conditions of this Agreement,
SP Ltd. shall pay to TBC royalties [*] in an amount equal to:
    (i) [*];
    (ii) [*];
    and (iii).

The parties acknowledge and agree that for purposes of this Agreement worldwide
annual Net Sales shall be determined by [*].

    (b)      Term of Royalty Obligation  [*].
    (c)      Third Party Licenses  [*]
    (d)      Royalties for Bulk Compound  [*]
    (e)      Compulsory Licenses  [*]

-----------------
[*] Designates portions of this document that have been omitted pursuant to
    a request for confidential treatment filed with the Commission.


                                     -11-

<PAGE>   17

5.7 Reports; Payment of Royalty; Payment Exchange Rate and Currency Conversions

    (a) [*]

    (b) Method of Payment Payments to be made by SP Ltd. to TBC under this
Agreement [*].

5.8 Maintenance of Records; Audits

    (a) Record keeping by SP Ltd. SP Ltd. and its Affiliates shall keep
complete and accurate records in sufficient detail to enable the royalties
payable hereunder to be determined. [*]

    (b) [*]

    (c) Record Keeping by Sublicensee SP Ltd. shall include in each sublicense
granted by it pursuant to this Agreement a provision requiring the sublicensee
to make reports to SP Ltd., to keep and maintain records of sales made pursuant
to such sublicense and to grant access to such records by TBC's independent
accountant [*].

    (d) Confidentiality TBC shall treat all financial information subject to
review under this Section 5.8, or under any sublicense agreement, in accordance
with the confidentiality provisions of Article VII of this Agreement, [*].

5.9 Income Tax Withholding If at any time, any jurisdiction within the
Territory requires the withholding of income taxes or other taxes imposed upon
payments set forth in this Article V, [*].

5.10     Direct Affiliate Licenses  [*]

5.11 Animal Health Indications In the event that SP Ltd. and/or its Affiliates
develop a Licensed Compound or Licensed Product for any animal health
indication, the parties will negotiate, in good faith, reduced milestones and
royalty terms appropriate for such animal health product.

                              ARTICLE VI - PATENTS

6.1      Filing, Prosecution and Maintenance of Patents  [*]

6.2      [*]

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                                     -12-

<PAGE>   18

6.3      Enforcement

         (a) Notice and Discontinuance of Infringement In the event that either
SP Ltd. or TBC becomes aware of any alleged or threatened infringement in a
country in the Territory of any issued patent within the VLA-4 Patent Rights,
it will notify the other party in writing to that effect. [*].

         (b)   Continuance of Infringement  [*]

6.4      Infringement and Third Party Licenses

         (a)   Course of Action  [*]
         (b)   [*]
         (c)   [*]

6.5      Third Party Infringement Suit  [*]

6.6      Abandonment  [*]

6.7      Patent Term Restoration  [*]

6.8      Notices Regarding Patents  [*]

If to TBC:

         Texas Biotechnology Corporation
         7000 Fannin, 20th floor
         Houston, TX  77030
         Attn:  President

         with a copy to:

         Porter & Hedges, L.L.P.
         700 Louisiana, 35th Floor
         Houston, TX  77002-2764
         Attn:  Robert G. Reedy

If to SP Ltd.:

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                                     -13-

<PAGE>   19
         Schering-Plough Ltd.
         c/o Schering Corporation
         2000 Galloping Hill Road
         Kenilworth, New Jersey  07033
         Attn: Staff Vice President - Patents and Trademarks
         Fax No.: 908  298-5388

                 ARTICLE VII - CONFIDENTIALITY AND PUBLICATION

7.1      Confidentiality

         (a) Nondisclosure Obligation Each of TBC and SP Ltd. shall use any
Proprietary Information received by it from the other party only in accordance
with this Agreement and shall not disclose to any third party any such
Proprietary Information without the prior written consent of the other party.
The foregoing obligations shall survive the expiration or termination of this
Agreement for a period of ten (10) years. These obligations shall not apply to
Proprietary Information that:

                  (i) is  known  by the receiving party at the time of its
receipt, and not through a prior by the disclosing party, as documented by
business records;

                  (ii) is at the time of disclosure, or thereafter becomes,
published or otherwise part of the public domain without breach of this
Agreement by the receiving party;

                  (iii) is subsequently disclosed to the receiving party by a
third party who has the right to make such disclosure;

                  (iv) is independently developed by the receiving party or its
Affiliates outside of the Research Program and without use of the disclosing
party's Proprietary Information, and such independent development can be
documented by the receiving party;

                  (v) is disclosed to any institutional review board of any
entity conducting clinical trials with Licensed Compound(s) or Licensed
Product(s) or to any governmental or other regulatory agencies in order to
obtain patents or to gain approval to conduct clinical trials or to market
Licensed Compound and/or Licensed Product, provided that such disclosure may be
made only to the extent reasonably necessary to obtain such patents or
authorizations; or

                  (vi) is required to be disclosed by law, regulation, rule,
act or order of any governmental authority or agency to be disclosed, provided
that notice is promptly delivered to the other party in order to provide an
opportunity to seek a protective order or other similar order with respect to
such Proprietary Information and thereafter the receiving party discloses to
the

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                                     -14-

<PAGE>   20

requesting entity only the minimum information required to be disclosed in
order to comply with the request, whether or not a protective order or other
similar order is obtained by the other party.

         (b) Disclosure to Agents Notwithstanding the provisions of Section
7.1(a) and subject to the other terms of this Agreement, each of SP Ltd. and
TBC shall have the right to disclose Proprietary Information to their
respective sublicensees, agents, consultants, Affiliates or other third parties
(collectively "Agents") in accordance with this Section 7.1(b). Such disclosure
shall be limited only to those Agents directly involved in the research,
development, manufacturing, marketing or promotion of Licensed Compound or
Licensed Product (or for such Agents to determine their interest in performing
such activities) in accordance with this Agreement. Any such Agents must agree
in writing to be bound by confidentiality and non-use obligations essentially
the same as those contained in this Agreement. [*]

7.2 Return of Confidential Information Upon termination of this Agreement, the
receiving party will return all documents, and copies thereof, including those
in the possession of the receiving party's Agents pursuant to Section 7.1(b),
containing the disclosing party's Proprietary Information at any time upon
request of the disclosing party. However, the receiving party may retain one
copy of such documents in a secure location solely for the purposes of (i)
determining its obligations hereunder, (ii) complying with any applicable
regulatory requirements, or (iii) defending against any product liability
claim.

7.3 No Publicity A party may not use the name of the other party in any
publicity or advertising and may not issue a press release or otherwise
publicize or disclose any information related to the existence of this
Agreement or the terms or conditions hereof, except (i) on the advice of its
counsel as required by law (e.g., any Securities and Exchange Commission
filings and disclosures) and provided the party who will be disclosing such
information has consulted with the other party to the extent feasible prior to
such disclosure with respect to the substance of the disclosure; or (ii) as
consented to in advance by the other party in writing. The parties shall agree
on a form of initial press release that may be used by either party on an
ongoing basis to describe this Agreement.

7.4 Publication Each of SP Ltd. and TBC acknowledges the other party's interest
in publishing its results to obtain recognition within the scientific community
and to advance the

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                                     -15-

<PAGE>   21

state of scientific knowledge. Each party also recognizes the mutual interest
in obtaining valid patent protection and in protecting business interests and
trade secret information. [*]

                 ARTICLE VIII - REPRESENTATIONS AND WARRANTIES

8.1      Representations  and  Warranties  of Each Party Each of TBC and SP
Ltd.  hereby  represents,  warrants and covenants to the other party hereto as
follows:

         (a) it is a corporation duly organized and validly existing under the
laws of the state or other jurisdiction of its incorporation;

         (b) the execution, delivery and performance of this Agreement by such
party has been duly authorized by all requisite corporate action, subject only
to receipt of requisite boards of directors' approvals;

         (c) it has the power and authority to execute and deliver this
Agreement and to perform its obligations hereunder;

         (d) the execution, delivery and performance by such party of this
Agreement and its compliance with the terms and provisions hereof does not and
will not conflict with or result in a breach of any of the terms and provisions
of or constitute a default under (i) a loan agreement, guaranty, financing
agreement, agreement affecting a product or other agreement or instrument
binding or affecting it or its property; (ii) the provisions of its corporate
charter or other operative documents or bylaws; or (iii) any order, writ,
injunction or decree of any court or governmental authority entered against it
or by which any of its property is bound;

         (e) except for the governmental and Regulatory Approvals required to
market the Licensed Product in the Territory, the execution, delivery and
performance of this Agreement by such party does not require the consent,
approval or authorization of, or notice, declaration, filing or registration
with, any governmental or regulatory authority and the execution, delivery or
performance of this Agreement will not violate any law, rule or regulation
applicable to such party;

         (f) this Agreement has been duly authorized, executed and delivered
and constitutes such party's legal, valid and binding obligation enforceable
against it in accordance with its terms subject, as to enforcement, to
bankruptcy, insolvency, reorganization and other laws of general applicability
relating to or affecting creditors' rights and to the availability of
particular remedies under general equity principles; and

         (g) it shall comply with all applicable material laws and regulations
relating to its activities under this Agreement.

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                                     -16-

<PAGE>   22

8.2  TBC's Representations  TBC hereby represents, warrants and covenants to
SP Ltd. as follows:

         (a) to the best of TBC's knowledge, as of the Effective Date the VLA-4
Patent Rights and VLA-4 Know-How are subsisting and are not invalid or
unenforceable, in whole or in part;

         (b) as of the Effective Date it has the full right, power and
authority to grant all of the right, title and interest in the licenses [*]
granted under Article III hereof;

         (c) as of the Effective Date it has not assigned, transferred,
conveyed or otherwise encumbered, and during the term of this Agreement will
not assign, transfer, convey of otherwise encumber, its right, title and
interest in the VLA-4 Patent Rights or VLA-4 Know-How (except in accordance
with this Agreement);

         (d) to the best of TBC's knowledge, as of the Effective Date it is the
sole and exclusive owner of the VLA-4 Patent Rights and VLA-4 Know-How, all of
which is free and clear of any liens, charges and encumbrances, and no other
person, corporate or other private entity, or governmental entity or
subdivision thereof, has or shall have any claim of ownership with respect to
the VLA-4 Patent Rights and VLA-4 Know-How, whatsoever;

         (e) during the term of this Agreement, TBC shall not take any action
which would (i) create any liens, charges or encumbrances with respect to the
VLA-4 Patent Rights, VLA-4 Know-How [*] , whatsoever, or (ii) give rise to any
third party claim of ownership with respect to the VLA-4 Patent Rights, VLA-4
Know-How [*] whatsoever;

         (f) to the best of TBC's knowledge, as of the Effective Date the
licensed VLA-4 Patent Rights and VLA-4 Know-How, and the development,
manufacture, use, distribution, marketing, promotion and sale of
Licensed Compound and Licensed Products doe not interfere or infringe on
any intellectual property rights owned or possessed by any third party;

         (g) to the best of TBC's knowledge, except for the [*], as of
the Effective Date there are no third party pending patent applications
which, if issued, may cover the development, manufacture, use,
distribution, marketing, promotion or sals of Licensed Compounds or
Licensed Products;

         (h) as of the Effective Date there are no claims, judgments or
settlements against or owed by TBC or pending or threatened claims or
litigation against TBC relating to VLA-4 Patent Rights and VLA-4 Know-How;

         (i) it has disclosed to SP Ltd. all VLA-4 Know-How, [*] and other
relevant information required to be disclosed hereunder, including, without
limitation, information relating to the VLA-4 Patent Rights, Materials, [*],
VLA-4 Compounds, [*] and the Research Program;

         (j) as of the Effective Date, it is in compliance in all material
respects with any agreements with third parties and during the term of this
Agreement (i) it will use diligent efforts not to diminish the rights under the
VLA-4 Patent Rights and VLA-4 Know-How granted to SP Ltd. hereunder, including
without limitation, by not committing or permitting any actions or omissions
which would cause the breach of any agreements between itself and third parties
which provide for intellectual property rights applicable to the development,
manufacture, use, distribution, marketing, promotion or sale of Licensed
Compounds and/or Licensed Products, and (ii) it will provide SP Ltd. promptly
with notice of any such alleged breach; and

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                                     -17-

<PAGE>   23

         (k) during the term of this Agreement it will not use in any capacity,
in connection with any services to be performed under this Agreement, any
individual who has been debarred pursuant to the United States Food, Drug and
Cosmetic Act.

8.3 SP Ltd.'s Representations SP Ltd. hereby represents, warrants and covenants
to TBC as follows:

         (a) during the term of this Agreement it will not use in any capacity,
in connection with any services to be performed under this Agreement, any
individual who has been debarred pursuant to the United States Food, Drug and
Cosmetic Act;

         (b) to the best of SP Ltd.'s knowledge, as of the Effective Date it is
the sole and exclusive owner of the SP Ltd. Know-How, all of which is free and
clear of any liens, charges and encumbrances, and no other person, corporate or
other private entity, or governmental entity or subdivision thereof, has or
shall have any claim of ownership with respect to the SP Ltd. Know-How,
whatsoever; and

         (c) as of the Effective Date, it is in compliance in all material
respects with any agreements with third parties and during the term of this
Agreement (i) it will use diligent efforts not to diminish the rights under the
SP Ltd. Know-How granted to TBC hereunder, including without limitation, by not
committing or permitting any actions or omissions which would cause the breach
of any agreements between itself and third parties which provide for
intellectual property rights applicable to the development, manufacture, use or
sale of Licensed Compounds and/or Licensed Products, and (ii) it will provide
TBC promptly with notice of any such alleged breach.

8.4 No Inconsistent Agreements Neither party has in effect, and after the
Effective Date neither party shall enter into, any oral or written agreement or
arrangement that would be inconsistent with its obligations under this
Agreement.

8.5 Representation by Legal Counsel Each party hereto represents that it has
been represented by legal counsel in connection with this Agreement and
acknowledges that it has participated in the drafting hereof. In interpreting
and applying the terms and provisions of this Agreement, the parties agree that
no presumption shall exist or be implied against the party which drafted such
terms and provisions.

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                                     -18-

<PAGE>   24

            ARTICLE IX - INDEMNIFICATION AND LIMITATION ON LIABILITY

9.1 Indemnification by SP Ltd. SP Ltd. shall indemnify, defend and hold
harmless TBC and its Affiliates, and each of its and their respective
employees, officers, directors and agents (each, a "TBC Indemnified Party")
from and against any and all liability, loss, damage, cost, and expense
(including reasonable attorneys' fees), subject to the limitations in Section
9.5 (collectively, a "Liability") which a TBC Indemnified Party may incur,
suffer or be required to pay resulting from or arising out of (i) the
development, manufacture, promotion, distribution, use, marketing, sale or
other disposition of Licensed Compounds and/or Licensed Products by SP Ltd.,
its Affiliates or sublicensees, and (ii) any breach by SP Ltd. of any of its
representations, warranties and covenants contained in Sections 8.1 and 8.3
hereof. Notwithstanding the foregoing, SP Ltd. shall have no obligation under
this Agreement to indemnify, defend or hold harmless any TBC Indemnified Party
with respect to claims, demands, costs or judgments which result from the gross
negligence or willful misconduct of TBC, its Affiliates, or any of their
respective employees, officers, directors or agents.

9.2 Indemnification by TBC TBC shall indemnify, defend and hold harmless SP
Ltd. and its Affiliates, and each of its and their respective employees,
officers, directors and agents (each, a "SP Ltd. Indemnified Party") from and
against any Liability which a SP Ltd. Indemnified Party may incur, suffer or be
required to pay resulting from or arising in connection with (i) the
performance of the Research Program by TBC, its Affiliates, or any of their
respective employees, officers, directors or agents, and (ii) any breach by TBC
of any of its representations, warranties and covenants contained in Sections
8.1 and 8.2 hereof.

9.3 Conditions to Indemnification The obligations of the indemnifying party
under Sections 9.1 and 9.2 are conditioned upon the delivery of written notice
to the indemnifying party of any potential Liability promptly after the
indemnified party becomes aware of such potential Liability. The indemnifying
party shall have the right to assume the defense of any suit or claim related
to the Liability if it has assumed responsibility for the suit or claim in
writing; however, if in the reasonable judgment of the indemnified party, such
suit or claim involves an issue or matter which could have a materially adverse
effect on the business operations or assets of the indemnified party, the
indemnified party may retain control of the defense or settlement thereof by
providing written notice of such effect to the indemnifying party, but in no
event shall such action or notice be construed as a waiver of any
indemnification rights that the indemnified party may have at law or in equity.
If the indemnifying party defends the suit or claim, the indemnified

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<PAGE>   25

party may participate in (but not control) the defense thereof at its sole cost
and expense. The foregoing notwithstanding, the parties acknowledge and agree
that failure of the indemnified party to promptly notify the indemnifying party
of a potential Liability shall not constitute a waiver of, or result in the
loss of, such party's right to indemnification under Section 9.1 or 9.2, as
appropriate, except to the extent that the indemnifying party's rights, and/or
its ability to defend against such Liability, are materially prejudiced by such
failure to notify.

9.4 Settlements Neither party may settle a claim or action related to a
Liability without the consent of the other party, which consent shall not be
unreasonably withheld, if such settlement would impose any monetary obligation
on the other party or require the other party to submit to an injunction or
otherwise limit the other party's rights under this Agreement. Any payment made
by a party to settle any such claim or action shall be at its own cost and
expense.

9.5 Limitation of Liability With respect to any claim by one party against the
other arising out of the performance or failure of performance of the other
party under this Agreement, the parties expressly agree that the liability of
such party to the other party for such breach shall be limited under this
Agreement or otherwise at law or equity to direct damages only and in no event
shall a party be liable for punitive, exemplary or consequential damages.

9.6 Insurance Each party acknowledges and agrees that during the term of this
Agreement it shall maintain adequate insurance and/or a self-insurance program
for liability insurance, including products liability and contractual liability
insurance, to cover such party's obligations under this Agreement. Each party
shall provide the other party with evidence of such insurance and/or
self-insurance program, upon request.


                        ARTICLE X - TERM AND TERMINATION

10.1 Term and Expiration This Agreement shall be effective as of the Effective
Date and unless terminated earlier by mutual written agreement of the parties
or pursuant to Sections 10.2 or 10.3 below, the term of this Agreement shall
continue in effect [*] until the earlier to occur of (i) expiration of SP
Ltd.'s obligation to pay royalties under Article V hereof, or (ii) the
thirtieth (30th) anniversary of the Effective Date. Upon expiration of this
Agreement, [*].

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<PAGE>   26

10.2 Termination by SP Ltd.

     (a) SP Ltd.'s Right to Terminate Notwithstanding anything contained herein
to the contrary, SP Ltd. shall have the unilateral right to terminate this
Agreement, with or without cause, at any time by giving one hundred eighty (180)
days advance written notice to TBC. In the event of such termination, the rights
and obligations hereunder shall terminate; provided, however, that any payment
obligations due and owing as of the termination date shall continue.

     (b) Effect of Termination Notwithstanding anything contained herein to the
contrary, following any termination under Section 10.2(a), [*]:

[*]

10.3 Termination

     (a) Termination for Cause This Agreement may be terminated by notice by
either party at any time during the term of this Agreement:

         (i)  if the other party is in breach of its material obligations
hereunder and has not cured such breach within ninety (90) days after notice
requesting cure of the breach, or in the event that the breach cannot be
reasonably cured within such ninety (90) day period, has not initiated actions
reasonably expected to cure such breach within ninety (90) days after receipt
of notice and thereafter diligently pursues such actions to cure the breach; or

         (ii) upon the filing or institution of bankruptcy, reorganization,
liquidation or receivership proceedings, or upon an assignment of a substantial
portion of the assets for the benefit of creditors by the other party, or in
the event a receiver or custodian is appointed for such party's business, or if
a substantial portion of such party's business is subject to attachment or
similar process; provided, however, that in the case of any involuntary
bankruptcy proceeding such right to terminate shall only become effective if
the proceeding is not dismissed within sixty (60) days after the filing
thereof.

     (b)  Effect of Termination for Cause on License

         (i) Termination for Breach or Change of Control. In the event SP Ltd.
terminates this Agreement under Sections 10.3(a)(i) or 11.1(c), SP Ltd.'s
licenses pursuant to Sections 3.1 and 3.2 shall become fully paid-up, perpetual
licenses.

         (ii) Termination for Diligence Failure. In the event that TBC
terminates this Agreement under Sections 4.1(b) and/or 10.3(a)(i), then the
rights and licenses granted to SP Ltd. under Sections 3.1 and 3.2 of this
Agreement shall terminate and all rights to Licensed Compounds and Licensed
Products shall revert to TBC. In the event of such termination by TBC, SP Ltd.
shall grant to TBC a license to use SP Ltd. Know-How necessary to develop, make,
have made, use and sell Licensed Compounds or Licensed Products to which TBC
holds rights hereunder; provided, however, in the event that TBC successfully
develops Licensed Compounds or Licensed Products then TBC shall promptly notify
SP Ltd. to that effect. SP Ltd. shall thereafter have an exclusive option to
negotiate an exclusive license for commercial purposes to such Licensed
Compounds or Licensed Products. SP Ltd. shall exercise such option by advising
TBC, in writing, of its interest in obtaining an exclusive license to any
development. SP Ltd. shall exercise its option and negotiate such license
agreement within six (6) months of SP Ltd.'s receipt of notice of said
development. If SP Ltd. exercises its option and the parties fail, in good
faith, to execute a mutually acceptable license agreement within such six (6)
month period, TBC will be free to license its interests in the development to
any third party.

         (iii) Effect of Bankruptcy. In the event SP Ltd. terminates this
Agreement under Sections 10.3(a)(ii) or this Agreement is otherwise terminated
under Section 10.3(a)(ii), the parties agree that SP Ltd., as a licensee of
rights to intellectual property under this Agreement, shall retain and may fully
exercise all of its rights and elections under Title 11, including as set forth
in Section 11.8 hereof.

10.4 Effect of Termination Termination of this Agreement by either party
pursuant to Section 10.1, 10.2 or 10.3 hereof shall constitute termination of
the U.S. Agreement under the corresponding provisions thereof. [*].

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<PAGE>   27

10.5     [*]

[*]

                           ARTICLE XI - MISCELLANEOUS

11.1     Assignment/Change of Control

         (b)      [*]

         (c)      [*]

         (d)      [*]

         (e)      Definition of Change of Control. As used in this Section 11.1
the term "Change of Control" shall mean (i) any merger, reorganization,
consolidation or combination in which a party to this Agreement is not the
surviving corporation, or (ii) any "person" (within the meaning of Sections
13(d) and 14(d)(2) of the Securities Exchange Act of 1934), excluding Schering
and its Affiliates, is or becomes the beneficial owner, directly or indirectly,
of securities of the party representing 50% or more of either (a) the
then-outstanding shares of common stock of the party or its parent corporation,
or (b) the combined voting power of the party's then-outstanding voting
securities; or (iii) if individuals who as of the Effective Date constitute the
Board of Directors of the party or its parent corporation (the "Incumbent
Board") cease for any reason to constitute at least a majority of such Board of
Directors; provided, however, that any individual becoming a director subsequent
to the Effective Date whose election, or nomination for election by the party's
shareholders, was approved by a vote of at least a majority of the directors
then comprising the Incumbent Board shall be considered as though such
individual were a member of the Incumbent Board, but excluding, for this
purpose, any such individual whose initial assumption of office occurs as a
result of an actual or threatened election contest with respect to the election
or removal of directors or other actual or threatened solicitation of proxies or
consents by or on behalf of a person other than the Incumbent Board; or (iv)
approval by the shareholders of a party of a complete liquidation or the
complete dissolution of such party.

11.2 Governing Law This Agreement shall be governed, interpreted and construed
in accordance with the laws of the State of Delaware, without giving effect to
its conflict of law principles. The parties expressly exclude application of
the United Nations Convention for the International Sale of Goods. [*]

11.3 Waiver Any delay or failure in enforcing a party's rights under this
Agreement or any waiver as to a particular default or other matter shall not
constitute a waiver of such party's rights to the future enforcement of its
rights under this Agreement, nor operate to bar the exercise or enforcement
thereof at any time or times thereafter, excepting only as to an express
written and signed waiver as to a particular matter for a particular period of
time.

11.4 Independent Relationship Nothing herein contained shall be deemed to
create an employment, agency, joint venture or partnership relationship between
the parties hereto or any of their agents or employees, or any other legal
arrangement that would impose liability upon one party for the act or failure
to act of the other party. Neither party shall have any power to enter into any
contracts or commitments or to incur any liabilities in the name of, or on
behalf of, the other party, or to bind the other party in any respect
whatsoever.

11.5 Export Control This Agreement is made subject to any restrictions
concerning the export of products or technical information from the United
States of America which may be imposed upon or related to TBC or SP Ltd. from
time to time by the government of the United States of

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                                     -22-

<PAGE>   28

America. Furthermore, SP Ltd. agrees that it will not export, directly or
indirectly, any technical information acquired from TBC under this Agreement or
any products using such technical information to any country for which the
United States government or any agency thereof at the time of export requires
an export license or other governmental approval, without first obtaining the
written consent to do so from the Department of Commerce or other agency of the
United States government when required by an applicable statute or regulation.

11.6 Entire Agreement; Amendment This Agreement, including the Exhibits and
Schedules hereto and thereto, sets forth the complete, final and exclusive
agreement and all the covenants, promises, agreements, warranties,
representations, conditions and understandings between the parties hereto and
supersedes and terminates all prior agreements and understandings between the
parties with regard to the subject matter hereof in the Territory. There are no
covenants, promises, agreements, warranties, representations, conditions or
understandings, either oral or written, between the parties other than as are
set forth herein and therein. No subsequent alteration, amendment, change,
waiver or addition to this Agreement shall be binding upon the parties unless
reduced to writing and signed by an authorized officer of each party.

11.7 Notices Except as provided under Section 6.8 hereof, any notice required
or permitted to be given or sent under this Agreement shall be hand delivered
or sent by express delivery service or certified or registered mail, postage
prepaid, or by facsimile transmission (with written confirmation copy by
registered first-class mail) to the parties at the addresses and facsimile
numbers indicated below.

         If to TBC, to:

         Texas Biotechnology Corporation
         7000 Fannin, 20th floor
         Houston, TX  77030
         Attn:  President

         with a copy to:

         Porter & Hedges, L.L.P.
         700 Louisiana, 35th Floor
         Houston, TX  77002-2764
         Attn:  Robert G. Reedy

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<PAGE>   29

If to SP Ltd., to:

         Schering-Plough Ltd.
         Toepferstrasse 5
         6004 Lucerne
         Switzerland
         Attention: President
         Facsimile No.:  (011) (41) (41) 418 16 32

         and

         Schering-Plough Ltd.
         c/o Schering Corporation
         2000 Galloping Hill Road
         Kenilworth, New Jersey  07033
         Attention:  President, Business Development
         Facsimile No.:  (908) 298-5379
         Attention: Law Department - Staff Vice-President, Licensing
         Facsimile No.: (908) 298-2739

Any such notice shall be deemed to have been received on the earlier of the
date actually received or the date five (5) days after the same was posted or
sent. Either party may change its address or its facsimile number by giving the
other party written notice, delivered in accordance with this Section 11.7.

11.8 Provisions for Insolvency

     (a) Effect on Licenses All rights and licenses granted under or pursuant
to this Agreement by TBC to SP Ltd. are, for all purposes of Section 365(n)
of Title 11 of the United States Code (together with its foreign equivalents,
the "Insolvency Statute"), licenses of rights to "intellectual property" as
defined in the Insolvency Statute. TBC agrees during the term of this Agreement
to create and maintain current copies or, if not amenable to copying, detailed
descriptions or other appropriate embodiments, to the extent feasible, of all
such intellectual property. If a case is commenced by or against TBC under the
Insolvency Statute, then, unless and until this Agreement is rejected as
provided in the Insolvency Statute, TBC (in any capacity, including
debtor-in-possession) and its successors and assigns (including, without
limitation, an

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<PAGE>   30

Insolvency Statute Trustee (as defined therein)) shall, as SP Ltd. may elect in
a written request, immediately upon such request:

         (i) [*]

         (ii) [*]. <BR>

    (b) Rights to Intellectual Property If an Insolvency Statute case is
commenced by or against TBC, and this Agreement is rejected as provided in the
Insolvency Statute, and SP Ltd. elects to retain its rights hereunder as
provided in the Insolvency Statute, then TBC (in any capacity, including
debtor-in-possession) and its successors and assigns (including, without
limitation, an Insolvency Statute Trustee) [*].

    (c) SP Ltd.'s Rights All rights, powers and remedies of SP Ltd.
provided herein are in addition to and not in substitution for any and all
other rights, powers and remedies now or hereafter existing at law or in equity
(including, without limitation, the Insolvency Statute). In the event of the
commencement of an Insolvency Statute case by or against TBC. SP Ltd., in
addition to the rights, power and remedies expressly provided herein, shall be
entitled to exercise all other such rights and powers and resort to all other
such remedies as may now or hereafter exist at law or in equity (including,
without limitation, the Insolvency Statute) in such event. The parties agree
that they intend the foregoing SP Ltd. rights to extend to the maximum extent
permitted by law, including, without limitation, for purposes of the Insolvency
Statute:

         (i) the right of access to any intellectual property (including all
embodiments thereof) of TBC, or any third party with whom TBC contracts to
perform an obligation of TBC under this Agreement, and, in the case of the
third party, which is necessary for the development, registration, manufacture
and marketing of Licensed Compounds and/or Licensed Products; and

         (ii) the right to contract directly with any third party described in
(i) to complete the contracted work.


    (d) Effect on U.S. Agreement The parties acknowledge and agree that the
occurrence of any event or series of events which gives effect to any of SP
Ltd.'s rights under Sections 11.8(a), 11.8(b) and/or 11.8(c) of this Agreement
shall have the same effect with respect to Schering Corporation's rights under
the corresponding provisions of the U.S. Agreement.

11.9 Force Majeure Failure of any party to perform its obligations under this
Agreement (except the obligation to make payments when properly due) shall not
subject such party to any liability or place them in breach of any term or
condition of this Agreement to the other party if such failure is due to any
cause beyond the reasonable control of such non-performing party ("force
majeure"), unless conclusive evidence to the contrary is provided. Causes of
non-

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<PAGE>   31

performance constituting force majeure shall include, without limitation,
acts of God, fire, explosion, flood, drought, war, riot, sabotage, embargo,
strikes or other labor trouble, failure in whole or in part of suppliers to
deliver on schedule materials, equipment or machinery, interruption of or delay
in transportation, a national health emergency or compliance with any order or
regulation of any government entity acting with color of right. The party
affected shall promptly notify the other party of the condition constituting
force majeure as defined herein and shall exert reasonable efforts to
eliminate, cure and overcome any such causes and to resume performance of its
obligations with all possible speed; provided that nothing herein shall
obligate a party to settle on terms unsatisfactory to such party any strike,
lockout or other labor difficulty, any investigation or other proceeding by any
public authority or any litigation by any third party. If a condition
constituting force majeure as defined herein exists for more than [*], the
parties shall meet to negotiate a mutually satisfactory resolution to the
problem, if practicable. If the parties cannot in good faith reach a
satisfactory resolution to the problem [*].

11.10 Severability If any provision of this Agreement is declared illegal,
invalid or unenforceable by a court having competent jurisdiction, it is
mutually agreed that this Agreement shall continue in accordance with its terms
except for the part declared invalid or unenforceable by order of such court,
provided, however, that in the event that the terms and conditions of this
Agreement are materially altered, the parties will, in good faith, renegotiate
the terms and conditions of this Agreement to reasonably substitute such
invalid or unenforceable provisions in light of the intent of this Agreement.

11.11 Counterparts This Agreement shall become binding when any one or more
counterparts hereof, individually or taken together, shall bear the signatures
of each of the parties hereto. This Agreement may be executed in any number of
counterparts, each of which shall be an original as against either party whose
signature appears thereon, but all of which taken together shall constitute but
one and the same instrument.

11.12 Captions The captions of this Agreement are solely for the convenience of
reference and shall not affect its interpretation.

11.13 Recording Each party shall have the right, at any time, to record,
register, or otherwise notify this Agreement in appropriate governmental or
regulatory offices anywhere in the world, and each party shall provide
reasonable assistance to the other in effecting such recording,

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<PAGE>   32

registering or notifying. The parties acknowledge that this Agreement may be
notified to the European Community for compliance with applicable laws.

11.14 Relationship to U.S. Agreement, Controlling Provisions The parties
acknowledge that this Agreement and the U.S. Agreement are intended to operate
together as a single worldwide agreement governing the rights and obligations
of TBC, SP Ltd. and Schering Corporation. For purposes of clarity and avoidance
of doubt, the parties agree that Article II and Sections 4.2, 4.3, 4.4 and 4.5
of this Agreement shall be governed by the corresponding provisions of the U.S.
Agreement. The parties further agree that SP Ltd.'s rights and obligations
under Article VI of this Agreement shall be exercised and performed by the
employees and/or agents of Schering Corporation having responsibility for
Schering Corporation's rights and obligations under Article VI of the U.S.
Agreement, and that all such activities will be performed in a coordinated
manner.

11.15 Further Actions Each party agrees to execute, acknowledge and deliver
such further instruments, and to do all other acts, as may be necessary or
appropriate in order to carry out the purposes and intent of this Agreement
including, without limitation, any filings with any antitrust agency which may
be required.

         IN WITNESS WHEREOF, this Agreement has been executed by the duly
authorized representatives of the parties as of the date set forth below.


TEXAS BIOTECHNOLOGY CORPORATION              SCHERING-PLOUGH LTD.


By:                                          By:
    ----------------------------                 ------------------------------
                                                    Thomas C. Lauda

Title:                                       Title: Director
       -------------------------                    ---------------------------

Date:                                        Date:
      --------------------------                   ----------------------------

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