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                                                                   EXHIBIT 10.28







                         [ALANEX CORPORATION LETTERHEAD]


July 17, 1996


Alexander Polinsky, Ph.D.
Alanex Corporation
3550 General Atomics Court
San Diego, California  92121

Dear Dr. Polinsky:

This letter will serve to memorialize our agreement regarding the payment of
severance benefits in the event of termination without cause at any time during
the period of your employment with Alanex Corporation (the "Company").

The Company agrees that if your employment with the Company is terminated
without cause, you shall be entitled to continuation of your base salary for a
period of two hundred seventy (270) days from the date of your termination, with
such base salary continuation to be at the rate of your current base salary in
effect as of the date of termination. In the event, however, that your
employment with the Company is terminated for cause, you shall be entitled to
receive only your accrued base salary and other accrued benefits required by law
to be paid to you, prorated to the date of termination. For purposes of this
letter, "for cause" termination shall be limited to the following: (1) engaging
in or in any way participating in any activity which is competitive with or
intentionally injurious to the Company or which violates any provisions of the
Proprietary Information and Inventions Agreement signed by you and the Company;
(2) the commission of any fraud against the Company or use or appropriation for
your personal use or benefit any funds or properties of the Company not so
authorized by the Board of Directors; (3) the conviction of a crime involving
dishonesty or moral turpitude; or (4) conduct which in good faith and reasonable
determination of the Board of Directors demonstrates gross unfitness to serve in
your position.

Notwithstanding the above agreement, the employment relationship between you and
the Company continues to be at-will. As such, you may terminate your employment
with the Company at any time and for any reason whatsoever simply by notifying
the Company of your intent to do so. In the event that you terminate the
employment relationship with the Company for any reasons whatsoever, you will
not be entitled to any severance payment 
   2
Alexander Polinsky, Ph.D.
July 17, 1996
Page Two

provided for hereunder. Likewise, the Company may terminate your employment at
any time and for any reason whatsoever, with or without cause or advance notice.
This at-will employment relationship cannot be changed except in a writing
signed by an authorized officer of the Company.

Very truly yours,

ALANEX CORPORATION


By: /s/ Marvin R. Brown
    ---------------------------------
Name:      Marvin R. Brown
Title:     Chief Executive Officer


ACCEPTED BY:



/s/ Alexander Polinsky
- -------------------------------------
Alexander Polinsky, Ph.D.

Dated:     July 17, 1996