<PAGE>   1
                               AMENDMENT NO. 1 TO

                          EXECUTIVE SERVICES AGREEMENT

         THIS AMENDMENT NO. 1 (THE "AMENDMENT"), is made and entered into as of
July 1, 1999, to that certain Executive Services Agreement (the "Agreement"),
dated as of July 1, 1997, by and between ZymeTx, Inc., a Delaware corporation
(the "Company"), and Peter G. Livingston ("Livingston"). Unless otherwise
defined herein, capitalized terms used but not defined herein shall have the
meaning set forth in the Agreement and the Agreement shall be amended to
incorporate any additional definitions provided for in this Amendment.

                               W I T N E S S E T H

         WHEREAS, Livingston is currently serving as President and Chief
Executive Officer of the Company; and

         WHEREAS, on July 24, 1996, the Company and Oklahoma Medical Research
Foundation ("OMRF") entered into that certain Employee Services Agreement (the
"OMRF Agreement"), pursuant to which, among other things, OMRF has leased the
services of Livingston to the Company;

         WHEREAS, on July 1, 1997, Livingston and the Company entered into the
Agreement, a copy of which is attached hereto as Annex "A";

         WHEREAS, on April 14, 1999, the Company and Livingston entered into
that certain Severance Compensation Agreement (the "Severance Agreement"), a
copy of which is attached hereto as Annex "B";

         WHEREAS, the Company and Livingston desire to enter into this Amendment
in order to ensure Livingston's continued service to the Company and to
acknowledge the terms of the Severance Agreement;

         NOW THEREFORE, in consideration of the mutual promises and agreements
herein contained, and other good and valuable consideration, the adequacy of
which is hereby acknowledged, the parties hereby agree as follows:

         1. AMENDMENT OF TERMINATION DATE. Section 2 of the Agreement is hereby
amended to read in its entirety as follows:

                           2. Term of Service. The term of Livingston's service
                  under this Agreement (the "Term"), which commenced on July 1,
                  1997 (the "Commencement Date"), shall continue through and
                  expire on July 1, 2000 (the "Termination Date"), unless
                  earlier terminated as herein provided.

         2. ACKNOWLEDGMENT OF SEVERANCE AGREEMENT. The parties hereto: (i)
acknowledge the terms of the Severance Agreement; (ii) agree to the
incorporation of such terms herein by reference thereto; and (iii) agree that
the terms of the Severance Agreement shall govern the termination of
Livingston's employment following a "Change in Control" (as such term is defined
in the Severance Agreement).

         3. SCOPE OF AMENDMENT. Except as amended hereby, all provisions of the
Agreement shall remain in full force and effect.



<PAGE>   2


         4. COUNTERPARTS. This Agreement may be executed in two or more
counterparts, each of which shall be deemed an original but all of which
together shall constitute one and the same instrument.

         5. HEADINGS. The headings in this Agreement are for reference purposes
only and shall not in any way affect the meaning or interpretation of this
Agreement.

         IN WITNESS WHEREOF, the parties have executed this Agreement as of the
date first above written.

COMPANY:                                     ZYMETX, INC.



                                             By:
                                                --------------------------------
                                                     James R. Tolbert III,
                                                     Chairman


LIVINGSTON:
                                             -----------------------------------
                                             Peter G. Livingston





                                       -2-