Exhibit
10.15




STOCK
OPTION AGREEMENT
 
 (Non-Employee
Director Stock Option)
 
 This Stock Option
Agreement (this “Agreement”), effective as of _____________ (the “Grant
Date”), is by and between Lexicon Pharmaceuticals,
Inc., a Delaware corporation (the “Company”), and _______________
(“Optionee”).
 
 To carry
out the purposes of the Lexicon Pharmaceuticals, Inc. Non-Employee Directors’
Stock Option Plan (the “Plan”), by providing Optionee the opportunity to
purchase shares of Common Stock, par value $0.001 per share, of the Company
(“Stock”), and in consideration of the mutual agreements and other matters set
forth herein and in the Plan, the Company and Optionee hereby agree as
follows:
 
 1.           Grant of
Option.  The Company hereby grants to Optionee the right and
option (the “Option”) to purchase all or any part of an aggregate of [10,000 or 20,000
(for annual grant)] [30,000 (for initial grant)] shares of Stock, on the
terms and conditions set forth in this Agreement and in the Plan.  The
Option shall be treated as a non-statutory stock option and not as an “incentive
stock option” within the meaning of section 422(b) of the Internal Revenue Code
of 1986, as amended (the “Code”).
 
 2.           Exercise
Price.  The price at which Optionee may purchase Stock upon
exercise of the Option (the “Exercise Price”) shall be $_______ per share, which
has been determined to be the Fair Market Value (as defined in the Plan) of the
Stock on the Grant Date.  The Exercise Price is subject to adjustment
under certain circumstances as provided in the Plan.
 
 3.           Term.  The
Option shall expire on the 10th anniversary of the Grant Date, subject to
earlier termination under the circumstances specified in Section 8 of this
Agreement.
 
 4.           Exercisability and
Vesting.  Subject to the terms and conditions set forth in this
Agreement and the Plan, the Option may be exercised, in whole or in part, at any
time and from time to time during the term of the Option, to purchase the number
of shares of Stock that have vested and become exercisable in accordance with
this Agreement.  The Option shall vest and become exercisable with
respect to [1/12 of the
total number of shares of Stock subject to the Option each month after grant for
12 months after the Grant Date (Use with annual grants)] [1/60 of the total
number of shares of Stock subject to the Option each month after grant for five
years after the Grant Date (Use with initial grants)]; provided that, such vesting
schedule may be accelerated upon a change in control of the Company pursuant to
the provisions of the Plan and; provided further, that, upon
the termination of Optionee’s Continuous Service (as defined in the Plan), the
Option shall cease to vest and shall terminate with respect to all shares of
Stock that have not vested and become exercisable prior to such
time.
 
 5.           Procedures for
Exercise.  Subject to the terms and conditions set forth in
this Agreement and the Plan, the Option may be exercised by delivery to the
Company at its principal executive office of (i) written notice addressed to the
Secretary of the Company specifying the number of shares of Stock as to which
the Option is being exercised and (ii) payment in full of the Exercise Price for
such shares.  The Exercise Price shall be paid in cash or in such
other manner as may be authorized by the administrator of the Plan in accordance
with the terms of the Plan.  If the offering, sale and delivery of the
shares of Stock issuable upon exercise of the Option have not been registered
under the Securities Act of 1933 (the “Securities Act”), the Company may require
Optionee, as a condition to Optionee’s exercise of the Option, to enter into a
stock purchase agreement containing such representations and warranties as the
Company may deem necessary to permit the issuance of the Stock purchased upon
exercise of the Option in compliance with the Securities Act and applicable
state securities laws.
 
 
 6.           No Rights of Ownership in
Stock Before Issuance.  No person shall be entitled to the
rights and privileges of stock ownership with respect to any shares of Stock
issuable upon exercise of the Option until such shares have been issued in
accordance with the terms of this Agreement and the Plan.
 
 7.           Non-Transferability.  The
Option may not be transferred by Optionee otherwise than (i) by will or the laws
of descent and distribution, by instrument to an inter vivos or testamentary
trust or by gift to a member of Optionee’s immediate family, in each case in
accordance with the terms of the Plan, or (ii) pursuant to a qualified domestic
relations order (as defined in Title I of the Employee Retirement Income
Security Act of 1974, as amended, or the rules thereunder).
 
 8.           Termination of
Option.  If Optionee’s Continuous Service is terminated for any
reason other than the Disability (as defined in the Plan) or death of Optionee,
the Option shall remain exercisable, with respect to the shares of Stock that
had vested under the terms of this Agreement before the date of such
termination, for a period of six months after the date of such termination
(subject to extension as provided in the Plan, but in no event later than the
expiration date of the Option specified in Section 3 of this Agreement),
following which six-month period this Agreement and Optionee’s right to exercise
the Option shall terminate.  If Optionee’s Continuous Service is
terminated because of Disability of Optionee, the Option shall remain
exercisable, with respect to the shares of Stock that had vested under the terms
of this Agreement before the date of such termination, for a period of 12 months
after the date of such termination (but in no event later than the expiration
date of the Option specified in Section 3 of this Agreement), following which
12-month period this Agreement and Optionee’s right to exercise the Option shall
terminate.  If (i) Optionee’s Continuous Service is terminated because
of death of Optionee or (ii) Optionee dies within the three-month period after
the termination of Optionee’s Continuous Service for a reason other than death,
the Option shall remain exercisable, with respect to the shares of Stock that
had vested under the terms of this Agreement before the date of death, for a
period of 18 months after the date of such termination (but in no event later
than the expiration date of the Option specified in Section 3 of this
Agreement), following which 18-month period this Agreement and the right to
exercise the Option shall terminate.  Notwithstanding the foregoing,
if the Optionee is removed from the Company’s Board of Directors for cause in
accordance with the Company’s Bylaws, this Agreement and Optionee’s right to
exercise any portion of the Option, whether or not vested, shall terminate at
the commencement of business on the date of such removal.
 
 9.           Withholding of
Tax.   To the extent that the Company is required under
applicable federal or state income tax laws to withhold any amount on account of
any present or future tax imposed as a result of the exercise of the Option,
Optionee shall pay the Company, at the time of such exercise, funds in an amount
sufficient to permit the Company to satisfy such withholding obligations in
full.  If Optionee fails to pay such amount, the Company shall be
authorized (i) to withhold from any cash remuneration then or thereafter payable
to Optionee any tax required to be withheld or (ii) to refuse to issue or
transfer any shares otherwise required to be issued pursuant to the terms of
this Agreement.
 
 10.           Status of
Stock.  (a)  Unless the offering, sale and delivery
of the shares of Stock issuable upon exercise of the Option have been registered
under the Securities Act, Optionee agrees that any shares of Stock purchased
upon exercise of the Option shall be acquired for investment without a view to
distribution, within the meaning of the Securities Act, and shall not be sold,
transferred, assigned, pledged or hypothecated in the absence of an effective
registration statement under the Securities Act and applicable state securities
laws or an applicable exemption from the registration requirements of the Act
and any applicable state securities laws.  Optionee further agrees
that the shares of Stock which Optionee may acquire by exercising the Option
will not be sold or disposed of in any manner which would constitute a violation
of any other applicable federal or state securities laws.  In
addition, Optionee agrees (i) that the certificates representing the shares of
Stock issued under this Agreement may bear such legend or legends as the
administrator of the Plan deems appropriate in order to assure compliance with
applicable securities laws, and (ii) that the Company may give instruction to
its transfer agent, if any, to stop transfer of the shares of Stock issued under
this Agreement on the stock transfer records of the Company, if such proposed
transfer would, in the opinion of counsel to the Company, constitute a violation
of any applicable securities law or any such agreements.
 2
 
 (b)           Optionee
further agrees that the Option granted herein shall be subject to the
requirement that if at any time the administrator of the Plan shall determine,
in its discretion, that the listing, registration or qualification of the shares
of Stock subject to such Option upon any securities exchange or market or under
any state or federal law, or the consent or approval of any governmental
regulatory body, is necessary or desirable as a condition of, or in connection
with, the purchase or issuance of shares of Stock hereunder, such Option may not
be exercised in whole or in part unless such listing, registration,
qualification, consent or approval shall have been effected or obtained free of
any conditions not reasonably acceptable to the  administrator of the
Plan.
 
 11.           Stock Option
Plan.  The Plan, a copy of which is available for inspection by
Optionee or other persons entitled to exercise this Option at the Company’s
principal executive office during business hours, is incorporated by reference
in this Agreement.  The Option is subject to, and the Company and
Optionee agree to be bound by, all of the terms and conditions of the Plan. In
the event of a conflict between this Agreement and the Plan, the terms of the
Plan shall control.  Subject to the terms of the Plan, the
administrator of the Plan shall have authority to construe the terms of this
Agreement, and the determinations of the administrator of the Plan shall be
final and binding on Optionee and the Company.
 
 12.           Binding
Agreement.  This Agreement shall be binding upon and inure to
the benefit of any successors to the Company and all persons lawfully claiming
under Optionee.
 
 13.           Governing
Law.  This Agreement and all actions taken hereunder shall be
governed by and construed in accordance with the laws of the State of
Delaware.
 
 IN
WITNESS WHEREOF, the Company has caused this Agreement to be duly executed and
Optionee has executed this Agreement as of the day and year first above
written.
 
 Lexicon
      Pharmaceuticals, Inc.By:Arthur
      T. Sands, M.D., Ph.D.President
      and Chief Executive OfficerOptionee[Name]