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                                                                 Exhibit 10.51



                                   January 1, 1997

Larry Bymaster
2987 Calle Frontera
San Clemente, CA 92673

    Re:  EMPLOYMENT TERMS

         Dear Larry:

         _This will confirm our understanding with respect to your employment
with Xytronyx, Inc. (the "Company").

         _The term of your employment shall be for a period of up to two years
beginning on the date first set forth above (the "Commencement Date").  During
your employment from the Commencement Date until December 31, 1997, you shall be
paid a salary of $187,000 per annum, and during your employment from January 1,
1998 until December 31, 1998, you shall be paid a salary of $100,000 per annum,
in each case subject to a Consultancy Offset and the other terms and conditions
described below.

         _The Company agrees that during your employment with the Company you
shall be entitled to provide outside consultancy services that do not in any way
compete with the Company or conflict with your obligations as an employee of the
Company.  To the extent that your income from any such consultancy exceeds
$187,000 during any calendar year of your employment with the Company, your
salary shall be reduced by such excess amount (a "Consultancy Offset").  You
agree to provide the Company with all information in connection with any such
consultancy as the Company shall reasonably request, including documentation to
confirm any income you earned in respect thereof.  If you obtain outside
employment other than with the Company prior to December 31, 1998, your
employment with the Company shall terminate and you shall be entitled to no
further benefits from the Company.

         _On the date of the Company's first Board meeting following your
execution of this letter, you shall be granted Options to purchase 25,000 shares
of the Company's common stock at the fair market value on the date of issuance,
exercisable for 7 years and vesting bi-annually over a period of two years.  In
addition, to the extent permitted by applicable law, all of your current options
shall vest 100% upon the termination of your employment with the Company and
shall remain exercisable for the duration of their term.

         _You agree that as a condition to your employment, you shall be
available for special projects and such other duties as may be reasonably
requested by the Chairman or Board of Directors of the Company; provided,
however, that in no event will the Company require you to work more than 30
hours per week.  You shall be reimbursed for your reasonable expenses performed
in connection with your employment in accordance with Company policies in effect
from time to time
_

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         This letter contains and constitutes the entire agreement between
ourselves canceling and superseding any prior understandings and agreements;
provided, however, that you agree to enter into such other agreements with the
Company, including Confidentiality Agreements, NonCompete Agreements and other
customary agreements, as may be reasonably requested by the Company.  [The
employment terms described in this letter shall be effective upon the approval
of the Company's Board at its first meeting following your execution of this
letter.]

                                            Very truly yours,

                                            Xytronyx, Inc.


                                            By:
                                               --------------------
                                               H. Laurence Shaw
                                               Chairman and CEO

Agreed and Accepted:


-----------------------
Mr. Larry Bymaster