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                                                                    EXHIBIT 10.6

                          SIGNAL PHARMACEUTICALS, INC.

                 2000 NON-EMPLOYEE DIRECTORS' STOCK OPTION PLAN


                          ADOPTED ON FEBRUARY 16, 2000
                 APPROVED BY STOCKHOLDERS _______________, 2000

                      EFFECTIVE DATE: _______________, 2000
                             TERMINATION DATE: NONE

1.      PURPOSES.

        (a) ELIGIBLE OPTION RECIPIENTS. The persons eligible to receive Options
are the Non-Employee Directors of the Company.

        (b) AVAILABLE OPTIONS. The purpose of the Plan is to provide a means by
which Non-Employee Directors may be given an opportunity to benefit from
increases in value of the Common Stock through the granting of Nonstatutory
Stock Options.

        (c) GENERAL PURPOSE. The Company, by means of the Plan, seeks to retain
the services of its Non-Employee Directors, to secure and retain the services of
new Non-Employee Directors and to provide incentives for such persons to exert
maximum efforts for the success of the Company and its Affiliates.

2.      DEFINITIONS.

        (a) "AFFILIATE" means any parent corporation or subsidiary corporation
of the Company, whether now or hereafter existing, as those terms are defined in
Sections 424(e) and (f), respectively, of the Code.

        (b) "ANNUAL GRANT" means an Option granted annually to all Non-Employee
Directors who meet the specified criteria specified in subsection 6(b) of the
Plan.

        (c) "ANNUAL MEETING" means the annual meeting of the stockholders of the
Company.

        (d) "BOARD" means the Board of Directors of the Company.

        (e) "CODE" means the Internal Revenue Code of 1986, as amended.

        (f) "COMMON STOCK" means the common stock of the Company.

        (g) "COMPANY" means SIGNAL PHARMACEUTICALS, INC., a Delaware
corporation.

        (h) "CONSULTANT" means any person, including an advisor, (i) engaged by
the Company or an Affiliate to render consulting or advisory services and who is
compensated for such services or (ii) who is a member of the Board of Directors
of an Affiliate. However, the


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term "Consultant" shall not include either Directors of the Company who are not
compensated by the Company for their services as Directors or Directors of the
Company who are merely paid a director's fee by the Company for their services
as Directors.

        (i) "CONTINUOUS SERVICE" means that the Optionholder's service with the
Company or an Affiliate, whether as an Employee, Director or Consultant, is not
interrupted or terminated. The Optionholder's Continuous Service shall not be
deemed to have terminated merely because of a change in the capacity in which
the Optionholder renders service to the Company or an Affiliate as an Employee,
Consultant or Director or a change in the entity for which the Optionholder
renders such service, provided that there is no interruption or termination of
the Optionholder's Continuous Service. For example, a change in status from a
Non-Employee Director of the Company to a Consultant of an Affiliate or an
Employee of the Company will not constitute an interruption of Continuous
Service. The Board or the chief executive officer of the Company, in that
party's sole discretion, may determine whether Continuous Service shall be
considered interrupted in the case of any leave of absence approved by that
party, including sick leave, military leave or any other personal leave.

        (j) "DIRECTOR" means a member of the Board of Directors of the Company.

        (k) "DISABILITY" means the permanent and total disability of a person
within the meaning of Section 22(e)(3) of the Code.

        (l) "EMPLOYEE" means any person employed by the Company or an Affiliate.
Mere service as a Director or payment of a director's fee by the Company or an
Affiliate shall not be sufficient to constitute "employment" by the Company or
an Affiliate.

        (m) "EXCHANGE ACT" means the Securities Exchange Act of 1934, as
amended.

        (n) "FAIR MARKET VALUE" means, as of any date, the value of the Common
Stock determined as follows:

               (i) If the Common Stock is listed on any established stock
exchange or traded on the Nasdaq National Market or the Nasdaq SmallCap Market,
the Fair Market Value of a share of Common Stock shall be the closing sales
price for such stock (or the closing bid, if no sales were reported) as quoted
on such exchange or market (or the exchange or market with the greatest volume
of trading in the Common Stock) on the last market trading day prior to the day
of determination, as reported in The Wall Street Journal or such other source as
the Board deems reliable.

               (ii) In the absence of such markets for the Common Stock, the
Fair Market Value shall be determined in good faith by the Board.

        (o) "INITIAL GRANT" means an Option granted to a Non-Employee Director
who meets the criteria specified in subsection 6(a) of the Plan.

        (p) "IPO DATE" means the effective date of the initial public offering
of the Common Stock.


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        (q) "NON-EMPLOYEE DIRECTOR" means a Director who is not an Employee.

        (r) "NONSTATUTORY STOCK OPTION" means an Option not intended to qualify
as an incentive stock option within the meaning of Section 422 of the Code and
the regulations promulgated thereunder.

        (s) "OFFICER" means a person who is an officer of the Company within the
meaning of Section 16 of the Exchange Act and the rules and regulations
promulgated thereunder.

        (t) "OPTION" means a Nonstatutory Stock Option granted pursuant to the
Plan.

        (u) "OPTION AGREEMENT" means a written agreement between the Company and
an Optionholder evidencing the terms and conditions of an individual Option
grant. Each Option Agreement shall be subject to the terms and conditions of the
Plan.

        (v) "OPTIONHOLDER" means a person to whom an Option is granted pursuant
to the Plan or, if applicable, such other person who holds an outstanding
Option.

        (w) "PLAN" means this SIGNAL PHARMACEUTICALS, INC. 2000 Non-Employee
Directors' Stock Option Plan.

        (x) "RULE 16b-3" means Rule 16b-3 promulgated under the Exchange Act or
any successor to Rule 16b-3, as in effect from time to time.

        (y) "SECURITIES ACT" means the Securities Act of 1933, as amended.

3.      ADMINISTRATION.

        (a) ADMINISTRATION BY BOARD. The Board shall administer the Plan unless
and until the Board delegates administration to a Committee, as provided in
subsection 3(c).

        (b) POWERS OF BOARD. The Board shall have the power, subject to, and
within the limitations of, the express provisions of the Plan:

               (i) To determine the provisions of each Option to the extent not
specified in the Plan.

               (ii) To construe and interpret the Plan and Options granted under
it, and to establish, amend and revoke rules and regulations for its
administration. The Board, in the exercise of this power, may correct any
defect, omission or inconsistency in the Plan or in any Option Agreement, in a
manner and to the extent it shall deem necessary or expedient to make the Plan
fully effective.

               (iii) To amend the Plan or an Option as provided in Section 12.

               (iv) Generally, to exercise such powers and to perform such acts
as the Board deems necessary or expedient to promote the best interests of the
Company that are not in conflict with the provisions of the Plan.


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        (c) DELEGATION TO COMMITTEE. The Board may delegate administration of
the Plan to a Committee or Committees of one (1) or more members of the Board,
and the term "Committee" shall apply to any person or persons to whom such
authority has been delegated. If administration is delegated to a Committee, the
Committee shall have, in connection with the administration of the Plan, the
powers theretofore possessed by the Board, including the power to delegate to a
subcommittee any of the administrative powers the Committee is authorized to
exercise (and references in this Plan to the Board shall thereafter be to the
Committee or subcommittee), subject, however, to such resolutions, not
inconsistent with the provisions of the Plan, as may be adopted from time to
time by the Board. The Board may abolish the Committee at any time and revest in
the Board the administration of the Plan.

        (d) EFFECT OF BOARD'S DECISION. All determinations, interpretations and
constructions made by the Board in good faith shall not be subject to review by
any person and shall be final, binding and conclusive on all persons.

4.      SHARES SUBJECT TO THE PLAN.

        (a) SHARE RESERVE. Subject to the provisions of Section 11 relating to
adjustments upon changes in the Common Stock, the Common Stock that may be
issued pursuant to Options shall not exceed in the aggregate two hundred fifty
thousand (250,000) shares of Common Stock.

        (b) REVERSION OF SHARES TO THE SHARE RESERVE. If any Option shall for
any reason expire or otherwise terminate, in whole or in part, without having
been exercised in full, the shares of Common Stock not acquired under such
Option shall revert to and again become available for issuance under the Plan.

        (c) SOURCE OF SHARES. The shares of Common Stock subject to the Plan may
be unissued shares or reacquired shares, bought on the market or otherwise.

5.      ELIGIBILITY.

        The Options as set forth in section 6 automatically shall be granted
under the Plan to all Non-Employee Directors.

6.      NON-DISCRETIONARY GRANTS.

        (a) INITIAL GRANTS. Without any further action of the Board, each
Non-Employee Director shall be granted an Initial Grant as follows: After the
IPO Date, each person who is elected or appointed for the first time to be a
Non-Employee Director automatically shall, upon the date of his or her initial
election or appointment to be a Non-Employee Director by the Board or
stockholders of the Company, be granted an Initial Grant to purchase twenty
thousand (20,000) shares of Common Stock on the terms and conditions set forth
herein.

        (b) ANNUAL GRANTS. Without any further action of the Board, a
Non-Employee Director shall be granted an Annual Grant as follows: On the day
following each Annual Meeting commencing with the Annual Meeting in 2000, (i)
each person (other than the Chairman of the Board of Directors of the Company)
who is a Non-Employee Director and has been a Non-Employee Director for at least
six (6) months automatically shall be granted an


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Annual Grant to purchase five thousand (5,000) shares of Common Stock on the
terms and conditions set forth herein, and (ii) the Chairman of the Board of
Directors of the Company (provided such Chairman of the Board is a Non-Employee
Director and has been a Non-Employee Director for at least six (6) months)
automatically shall be granted an Annual Grant to purchase seven thousand five
hundred (7,500) shares of Common Stock on the terms and conditions set forth
herein.

7.      OPTION PROVISIONS.

               Each Option shall be in such form and shall contain such terms
and conditions as required by the Plan. Each Option shall contain such
additional terms and conditions, not inconsistent with the Plan, as the Board
shall deem appropriate. Each Option shall include (through incorporation of
provisions hereof by reference in the Option or otherwise) the substance of each
of the following provisions:

        (a) TERM. No Option shall be exercisable after the expiration of ten
(10) years from the date it was granted.

        (b) EXERCISE PRICE. The exercise price of each Option shall be one
hundred percent (100%) of the Fair Market Value of the stock subject to the
Option on the date the Option is granted. Notwithstanding the foregoing, an
Option may be granted with an exercise price lower than that set forth in the
preceding sentence if such Option is granted pursuant to an assumption or
substitution for another option in a manner satisfying the provisions of Section
424(a) of the Code.

        (c) CONSIDERATION. The purchase price of stock acquired pursuant to an
Option may be paid, to the extent permitted by applicable statutes and
regulations, in any combination of the following methods:

               (i) By cash or check.

               (ii) Provided that at the time of exercise the Common Stock is
publicly traded and quoted regularly in The Wall Street Journal, by delivery of
already-owned shares of Common Stock either that the Optionholder has held for
the period required to avoid a charge to the Company's reported earnings
(generally six months) or that the Optionholder did not acquire, directly or
indirectly from the Company, that are owned free and clear of any liens, claims,
encumbrances or security interests, and that are valued at Fair Market Value on
the date of exercise. "Delivery" for these purposes shall include delivery to
the Company of the Optionholder's attestation of ownership of such shares of
Common Stock in a form approved by the Company. Notwithstanding the foregoing,
the Optionholder may not exercise the Option by tender to the Company of Common
Stock to the extent such tender would violate the provisions of any law,
regulation or agreement restricting the redemption of the Company's stock.

               (iii) Provided that at the time of exercise the Common Stock is
publicly traded and quoted regularly in The Wall Street Journal, pursuant to a
program developed under Regulation T as promulgated by the Federal Reserve Board
that, prior to the issuance of Common Stock, results in either the receipt of
cash (or check) by the Company or the receipt of


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irrevocable instructions to pay the aggregate exercise price to the Company from
the sales proceeds.

        (d) TRANSFERABILITY. An Option shall not be transferable except by will
or by the laws of descent and distribution and to such further extent as
permitted by the Rule as to Use of Form S-8 specified in the General
Instructions of the Form S-8 Registration Statement under the Securities Act,
and shall be exercisable during the lifetime of the Optionholder only by the
Optionholder. Notwithstanding the foregoing, the Optionholder may, by delivering
written notice to the Company, in a form satisfactory to the Company, designate
a third party who, in the event of the death of the Optionholder, shall
thereafter be entitled to exercise the Option.

        (e) EXERCISE SCHEDULE. The Option shall be exercisable as the shares of
Common Stock subject to the Opton vest.

        (f) EARLY EXERCISE. Notwithstanding the foregoing, the option may, but
need not, include a provision whereby the optionholder may elect at any time
while providing Continuous Service as a Non-Employee Director or employee of or
consultant to the Company or any Affiliate to exercise the option as to any part
of all of the shares subject to the option prior to the full vesting of the
option. Any unvested shares so purchased may be subject to a repurchase right in
favor of the Company or to any other restriction the Board determines to be
appropriate. The Company will not exercise its repurchase option until at least
six (6) months (or such longer or shorter period of time required to avoid a
charge to earnings for financial accounting purposes) have elapsed following
exercise of the Option unless the Board otherwise specifically provides in the
Option.

        (g) VESTING SCHEDULE. Options shall vest as follows:

               (i) Initial Grants shall provide for vesting of one thousand two
hundred fifty (1,250) of the shares of Common Stock subject to the Option at the
end of each three- (3-) month period after the date of the grant of the Option
over a period of four (4) years.

               (ii) Annual Grants shall vest in equal monthly installments after
the date of the grant of the Option over a period of one (1) year.

        (h) TERMINATION OF CONTINUOUS SERVICE. In the event an Optionholder's
Continuous Service terminates (other than upon the Optionholder's death or
Disability), the Optionholder may exercise his or her Option (to the extent that
the Optionholder was entitled to exercise it as of the date of termination) but
only within such period of time ending on the earlier of (i) the date three (3)
months following the termination of the Optionholder's Continuous Service, or
(ii) the expiration of the term of the Option as set forth in the Option
Agreement. If, after termination, the Optionholder does not exercise his or her
Option within the time specified in the Option Agreement, the Option shall
terminate.

        (i) EXTENSION OF TERMINATION DATE. If the exercise of the Option
following the termination of the Optionholder's Continuous Service (other than
upon the Optionholder's death or Disability) would be prohibited at any time
solely because the issuance of shares would violate the registration
requirements under the Securities Act, then the Option shall terminate on the
earlier of (i) the expiration of the term of the Option set forth in subsection
7(a) or (ii) the


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expiration of a period of three (3) months after the termination of the
Optionholder's Continuous Service during which the exercise of the Option would
not be in violation of such registration requirements.

        (j) DISABILITY OF OPTIONHOLDER. In the event an Optionholder's
Continuous Service terminates as a result of the Optionholder's Disability, the
Optionholder may exercise his or her Option (to the extent that the Optionholder
was entitled to exercise it as of the date of termination), but only within such
period of time ending on the earlier of (i) the date six (6) months following
such termination or (ii) the expiration of the term of the Option as set forth
in the Option Agreement. If, after termination, the Optionholder does not
exercise his or her Option within the time specified herein, the Option shall
terminate.

        (k) DEATH OF OPTIONHOLDER. In the event (i) an Optionholder's Continuous
Service terminates as a result of the Optionholder's death or (ii) the
Optionholder dies within the three-month period after the termination of the
Optionholder's Continuous Service for a reason other than death, then the Option
may be exercised (to the extent the Optionholder was entitled to exercise the
Option as of the date of death) by the Optionholder's estate, by a person who
acquired the right to exercise the Option by bequest or inheritance or by a
person designated to exercise the Option upon the Optionholder's death, but only
within the period ending on the earlier of (1) the date six (6) months following
the date of death or (2) the expiration of the term of such Option as set forth
in the Option Agreement. If, after death, the Option is not exercised within the
time specified herein, the Option shall terminate.

8.      COVENANTS OF THE COMPANY.

        (a) AVAILABILITY OF SHARES. During the terms of the Options, the Company
shall keep available at all times the number of shares of Common Stock required
to satisfy such Options.

        (b) SECURITIES LAW COMPLIANCE. The Company shall seek to obtain from
each regulatory commission or agency having jurisdiction over the Plan such
authority as may be required to grant Options and to issue and sell shares of
Common Stock upon exercise of the Options; provided, however, that this
undertaking shall not require the Company to register under the Securities Act
the Plan, any Option or any stock issued or issuable pursuant to any such
Option. If, after reasonable efforts, the Company is unable to obtain from any
such regulatory commission or agency the authority which counsel for the Company
deems necessary for the lawful issuance and sale of stock under the Plan, the
Company shall be relieved from any liability for failure to issue and sell stock
upon exercise of such Options unless and until such authority is obtained.

9.      USE OF PROCEEDS FROM STOCK.

        Proceeds from the sale of stock pursuant to Options shall constitute
general funds of the Company.

10.     MISCELLANEOUS.

        (a) STOCKHOLDER RIGHTS. No Optionholder shall be deemed to be the holder
of, or to have any of the rights of a holder with respect to, any shares subject
to such Option unless and


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until such Optionholder has satisfied all requirements for exercise of the
Option pursuant to its terms.

        (b) NO SERVICE RIGHTS. Nothing in the Plan or any instrument executed or
Option granted pursuant thereto shall confer upon any Optionholder any right to
continue to serve the Company as a Non-Employee Director or shall affect the
right of the Company or an Affiliate to terminate (i) the employment of an
Employee with or without notice and with or without cause, (ii) the service of a
Consultant pursuant to the terms of such Consultant's agreement with the Company
or an Affiliate or (iii) the service of a Director pursuant to the Bylaws of the
Company or an Affiliate, and any applicable provisions of the corporate law of
the state in which the Company or the Affiliate is incorporated, as the case may
be.

        (c) INVESTMENT ASSURANCES. The Company may require an Optionholder, as a
condition of exercising or acquiring stock under any Option, (i) to give written
assurances satisfactory to the Company as to the Optionholder's knowledge and
experience in financial and business matters and/or to employ a purchaser
representative reasonably satisfactory to the Company who is knowledgeable and
experienced in financial and business matters and that he or she is capable of
evaluating, alone or together with the purchaser representative, the merits and
risks of exercising the Option; and (ii) to give written assurances satisfactory
to the Company stating that the Optionholder is acquiring the stock subject to
the Option for the Optionholder's own account and not with any present intention
of selling or otherwise distributing the stock. The foregoing requirements, and
any assurances given pursuant to such requirements, shall be inoperative if
(iii) the issuance of the shares upon the exercise or acquisition of stock under
the Option has been registered under a then currently effective registration
statement under the Securities Act or (iv) as to any particular requirement, a
determination is made by counsel for the Company that such requirement need not
be met in the circumstances under the then applicable securities laws. The
Company may, upon advice of counsel to the Company, place legends on stock
certificates issued under the Plan as such counsel deems necessary or
appropriate in order to comply with applicable securities laws, including, but
not limited to, legends restricting the transfer of the stock.

        (d) WITHHOLDING OBLIGATIONS. The Optionholder may satisfy any federal,
state or local tax withholding obligation relating to the exercise or
acquisition of stock under an Option by any of the following means (in addition
to the Company's right to withhold from any compensation paid to the
Optionholder by the Company) or by a combination of such means: (i) tendering a
cash payment; (ii) authorizing the Company to withhold shares from the shares of
the Common Stock otherwise issuable to the Optionholder as a result of the
exercise or acquisition of stock under the Option, provided, however, that no
shares of Common Stock are withheld with a value exceeding the minimum amount of
tax required to be withheld by law; or (iii) delivering to the Company owned and
unencumbered shares of the Common Stock.

11.     ADJUSTMENTS UPON CHANGES IN STOCK.

        (a) CAPITALIZATION ADJUSTMENTS. If any change is made in the stock
subject to the Plan, or subject to any Option, without the receipt of
consideration by the Company (through merger, consolidation, reorganization,
recapitalization, reincorporation, stock dividend, dividend in property other
than cash, stock split, liquidating dividend, combination of shares, exchange of


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shares, change in corporate structure or other transaction not involving the
receipt of consideration by the Company), the Plan will be appropriately
adjusted in the class(es) and maximum number of securities subject both to the
Plan pursuant to subsection 4(a) and to the nondiscretionary Options specified
in Section 5, and the outstanding Options will be appropriately adjusted in the
class(es) and number of securities and price per share of stock subject to such
outstanding Options. The Board shall make such adjustments, and its
determination shall be final, binding and conclusive. (The conversion of any
convertible securities of the Company shall not be treated as a transaction
"without receipt of consideration" by the Company.)

        (b) CHANGE IN CONTROL--DISSOLUTION OR LIQUIDATION. In the event of a
dissolution or liquidation of the Company, then all outstanding Options shall
terminate immediately prior to such event.

        (c) CHANGE IN CONTROL--ASSET SALE, MERGER, CONSOLIDATION OR REVERSE
MERGER. In the event of (i) a sale, lease or other disposition of all or
substantially all of the assets of the Company, (ii) a merger or consolidation
in which the Company is not the surviving corporation or (iii) a reverse merger
in which the Company is the surviving corporation but the shares of Common Stock
outstanding immediately preceding the merger are converted by virtue of the
merger into other property, whether in the form of securities, cash or
otherwise, then with respect to Options held by Optionholders whose Continuous
Service has not terminated, the vesting of such Options (and, if applicable, the
time during which such Options may be exercised) shall be accelerated in full,
and the Options shall terminate if not exercised at or prior to such event. With
respect to any other Options outstanding under the Plan, such Options shall
terminate if not exercised prior to such event.

        (d) CHANGE IN CONTROL--SECURITIES ACQUISITION. In the event of an
acquisition by any person, entity or group within the meaning of Section 13(d)
or 14(d) of the Exchange Act, or any comparable successor provisions (excluding
any employee benefit plan, or related trust, sponsored or maintained by the
Company or an Affiliate) of the beneficial ownership (within the meaning of Rule
13d-3 promulgated under the Exchange Act, or comparable successor rule) of
securities of the Company representing at least fifty percent (50%) of the
combined voting power entitled to vote in the election of Directors and provided
that such acquisition is not a result of, and does not constitute a transaction
described in, subsection 11(c) hereof, then with respect to Options held by
Optionholders whose Continuous Service has not terminated, the vesting of such
Options and any shares of Common Stock acquired under such Options (and, if
applicable, the time during which such Options may be exercised) shall be
accelerated in full.

12.     AMENDMENT OF THE PLAN AND OPTIONS.

        (a) AMENDMENT OF PLAN. The Board at any time, and from time to time, may
amend the Plan. However, except as provided in Section 11 relating to
adjustments upon changes in stock, no amendment shall be effective unless
approved by the stockholders of the Company to the extent stockholder approval
is necessary to satisfy the requirements of Rule 16b-3 or any Nasdaq or
securities exchange listing requirements.


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        (b) STOCKHOLDER APPROVAL. The Board may, in its sole discretion, submit
any other amendment to the Plan for stockholder approval.

        (c) NO IMPAIRMENT OF RIGHTS. Rights under any Option granted before
amendment of the Plan shall not be impaired by any amendment of the Plan unless
(i) the Company requests the consent of the Optionholder and (ii) the
Optionholder consents in writing.

        (d) AMENDMENT OF OPTIONS. The Board at any time, and from time to time,
may amend the terms of any one or more Options; provided, however, that the
rights under any Option shall not be impaired by any such amendment unless (i)
the Company requests the consent of the Optionholder and (ii) the Optionholder
consents in writing.

13.     TERMINATION OR SUSPENSION OF THE PLAN.

        (a) PLAN TERM. The Board may suspend or terminate the Plan at any time.
No Options may be granted under the Plan while the Plan is suspended or after it
is terminated.

        (b) NO IMPAIRMENT OF RIGHTS. Suspension or termination of the Plan shall
not impair rights and obligations under any Option granted while the Plan is in
effect except with the written consent of the Optionholder.

14.     EFFECTIVE DATE OF PLAN.

        The Plan shall become effective on the IPO Date, but no Option shall be
exercised unless and until the Plan has been approved by the stockholders of the
Company, which approval shall be within twelve (12) months before or after the
date the Plan is adopted by the Board.

15.     CHOICE OF LAW.

        All questions concerning the construction, validity and interpretation
of this Plan shall be governed by the law of the State of California, without
regard to such state's conflict of laws rules.


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