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                                                                   EXHIBIT 10.70



                    FOURTH AMENDMENT TO CONSULTING AGREEMENT
    
     This FOURTH AMENDMENT TO CONSULTING AGREEMENT (the "Amendment") is made as
of the 1st day of January 1999 (the "Effective Date"), by and between JOHN M.
PIETRUSKI, an individual residing at 27 Paddock Lane, Colts Neck, New Jersey
07722 ("Consultant"), and TEXAS BIOTECHNOLOGY CORPORATION, a Delaware
corporation located at 7000 Fannin Street, Suite 1920, Houston, Texas 77030 (the
"Corporation").
    
     WHEREAS, the Corporation and Consultant have entered into that certain
Consulting Agreement dated January 1, 1992 (the "Agreement"), as set forth in
Exhibit "A" attached hereto and incorporated herein by reference; and
    
     WHEREAS, pursuant to the Agreement, the Corporation has retained Consultant
to provide consulting services to the Corporation with respect to corporate
governance, business development and other such matters; and
    
     WHEREAS, the Corporation and Consultant desire to amend the Agreement as
herein set forth.
    
     NOW, THEREFORE, for and in consideration of the foregoing and of the mutual
covenants contained herein, the parties hereto agree as follows:
    
     1. Definitions. If not otherwise defined herein, all capitalized terms used
herein shall have their respective meaning assigned to them in the Agreement.
    
     2. Amendment to Section 2. Effective as of the date hereof, Section 2 of
the Agreement is hereby amended by deleting paragraph (a) in its entirety and
substituting the following in lieu thereof:
    
          "(a) Consultant's retention under this agreement shall commence on the
     date hereof (the "Commencement Date") and shall end on the earliest of: (i)
     the death or disability (as defined herein) of Consultant, (ii) the
     termination of Consultant's retention by the Corporation for cause (as
     defined herein); or (iii) two years after the Effective Date. After the
     expiration of such two-year period, this Agreement may be renewed for
     additional periods on all the remaining terms and conditions set forth
     herein upon mutual agreement of Consultant and the Corporation."
    
     3. The terms and provisions set forth in this Amendment shall modify and
supersede all inconsistent terms and provisions set forth in the Agreement and
except as expressly modified and superseded by this Amendment, the terms and
provisions of the Agreement are ratified and confirmed and shall continue in
full force and effect. Corporation and Consultant agree that the Agreement as
amended shall continue to be legal, valid, binding and enforceable in accordance
with its terms.

    
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     4. Except as expressly modified or amended hereby, the terms and provisions
of the Agreement shall remain in force and effect in accordance with the terms
hereof, provided, however, that from and after the date hereof any reference to
the Agreement shall be deemed and construed as meaning the Agreement as amended
and modified hereby.
    
     IN WITNESS WHEREOF, the parties have executed this Amendment as of the day
and year first written above.
    
                                           CONSULTANT:
    
                                           /s/ JOHN M. PIETRUSKI
                                           -------------------------------------
                                           John M. Pietruski

                                           CORPORATION:
    
                                           TEXAS BIOTECHNOLOGY CORPORATION
   
                                           /s/ DAVID B. MCWILLIAMS
                                           -------------------------------------
                                           David B. McWilliams
                                           President and Chief Executive Officer

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                                   EXHIBIT "A"
    
                             (CONSULTING AGREEMENT)
    


See Exhibit 10.6(1) of the Company's 1998 Form 10-K.