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                                                                   EXHIBIT 10.63



         AMENDMENT TO THE 1995 NON-EMPLOYEE DIRECTOR STOCK OPTION PLAN


     The 1995 Non-Employee Director Stock Option Plan (the "Plan") of Texas
Biotechnology Corporation (the "Company") is hereby amended as follows
effective March 4, 1997.

1.   The first paragraph of Section 3 is amended to read as follows in its
     entirety:

     The stock subject to the Options and other provisions of the Plan shall be
shares of the Company's Common Stock, par value $.005 per share (the "Common
Stock"). The total amount of the Common Stock with respect to which Options may
be granted or issued pursuant to other provisions of the Plan shall not exceed
300,000 shares in the aggregate; provided, that the class and aggregate number
of shares which may be subject to the Options granted hereunder shall be
subject to adjustment in accordance with the provisions of Section 11 of this
Plan. Such shares may be treasury shares or authorized but unissued shares.

2.   Section 4(a) is amended to read as follows in its entirety:

     Directors Elected after the Effective Date of this Plan Upon their First
Election. Subject to the provisions of Section 18 hereof, for so long as this
Plan is in effect and shares are available for the grant of Options hereunder,
each person who shall be elected a Non-Employee Director after the Effective
Date of this Plan, excluding current Non-Employee Directors on the Effective
Date of this Plan, shall be granted, on the date of his or her first election, a
non-qualified Option to purchase 15,000 shares of Common Stock at an exercise
price equal to fair market value, of a Share of Common Stock, on the date of
grant (such number of shares being subject to the adjustments provided in
Section 11 of this Plan); provided, however, that no Options shall be granted
under this Subsection 4(a) for so long as a sufficient number of shares of
Common Stock remain available under the Company's existing Stock Option Plan for
Non-Employee Directors to permit the grant of options pursuant to the terms of
such plan. This Subsection 4(a) shall only apply to a Director the first time he
or she is elected Director of the Company and in no event shall this Plan
(whether by its sole operation or in operation with any other plans) entitle a
Director to receive, upon his initial election to the Board, options to purchase
a number of shares of Common Stock in excess of 15,000 shares of Common Stock at
an exercise price equal to fair market value of a Share of Common Stock on the
date of grant. Persons elected to be Directors for a second or any subsequent
term shall be granted options in accordance with Subsection 4(b) below.

3.   Section 4(b) is amended to read as follows in its entirety:

     Directors Elected after the Effective Date of this Plan Upon their Second
or any Subsequent Election. Subject to the provisions of Section 18 hereof, for
so long as this Plan is in effect and, shares are available for the grant of
Options hereunder, each person who shall be elected a Non-Employee Director for
his or her second (or any subsequent) term after their initial election to the
Board of Directors, including current Non-Employee Directors on the Effective
Date of this Plan, shall be granted, on the date of such election, a
non-qualified Option to purchase 7,500 shares of Common Stock at an exercise
price equal to the fair market value of a share of Common Stock on the date of
grant (such number of shares being subject to the adjustments provided in
Section 11 of this Plan); provided, however, that no Options shall be granted
under this Subsection 4(b) for so long as a sufficient number of shares of
Common Stock remain available under the Company's existing Stock Option Plan
for Non-Employee Directors to permit the grant of options pursuant to the terms
of such plan. This Subsection 4(b) shall only apply to a Director on his or her
second (or any subsequent) election to the Company's Board of Directors after
their initial election to the Board of Directors and in no event shall this
Plan (whether by its sole operation or in operation with any other plans)
entitle a Director to receive, upon any subsequent election to the Board,
options to purchase a number of shares of Common Stock in excess of 7,500
shares of Common Stock.