EXHIBIT 10.23

                                   TANOX, INC.

                 2000 NON-EMPLOYEE DIRECTORS' STOCK OPTION PLAN

      Adopted: February 17, 2000
      Approved by Stockholders: February 17, 2000
      Effective Date: As provided in the Plan

1. PURPOSES.

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

      (b) AVAILABLE OPTIONS. The Plan's purpose 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 Nonstatutory Stock Options grants.

      (c) GENERAL PURPOSE. The Company desires 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 Non-Employee Directors 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 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 criteria specified in subsection 6(b) of the Plan.

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

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

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

      (f) "COMMON STOCK" means the Company's common stock, $.01 par value per
share.
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      (g) "COMPANY" means Tanox, 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 these services or (ii) who is a member of the board of directors
of an Affiliate. The term "Consultant" shall not include either Directors who
are not compensated by the Company for their services as Directors, or Directors
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 terminate 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 services, provided that there is no interruption or termination of the
Optionholder's service. For example, a change in status without interruption
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 Company's chief executive officer, in that party's
sole discretion, may determine whether Continuous Service shall be considered
interrupted in the case of any approved leave of absence, including sick leave,
military leave or any other personal leave.

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

      (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 consultant 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 Small Cap Market,
      the Fair Market Value of a share of Common Stock shall be the closing
      sales price for the stock (or the closing bid, if no sales were reported)
      as quoted on the 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.
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            (ii) In the absence of these 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 Common Stock's initial
public offering.

      (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 under 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 Plan's terms and
conditions.

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

      (w) "PLAN" means this Tanox, 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. The
Board may not delegate the Plan's administration to a committee.

      (b) POWERS OF BOARD. The Board may, subject to, and within the limitations
of, the express provisions of the Plan:
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            (i) determine the provisions of each Option to the extent not
      specified in the Plan.

            (ii) construe and interpret the Plan and Options granted under it,
      and establish, amend and revoke rules and regulations for its
      administration;

            (iii) correct any defect, omission or inconsistency in the Plan or
      in any Option Agreement, in a manner and to the extent it deems necessary
      or expedient to make the Plan fully effective.

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

            (v) terminate or suspend the Plan as provided in Section 13.

            (vi) exercise such powers and perform such acts as the Board deems
      necessary or expedient to promote the best interests of the Company in
      accordance with the Plan's purposes and that do not conflict with the
      Plan's provisions.

      (c) 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 under this Plan may not exceed in the aggregate 500,000 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 the 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.
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6. NON-DISCRETIONARY GRANTS.

      (a) INITIAL GRANT. Without any further action of the Board, after the IPO
Date each person who is elected or appointed to be a Non-Employee Director for
the first time automatically shall, upon the date of his or her election or
appointment, be granted an Option to purchase 15,000 shares of Common Stock on
the terms and conditions set forth herein.

      (b) SUBSEQUENT GRANTS. Except as otherwise provided below, without any
further action of the Board, each person who is re-elected or re-appointed to be
a Non-Employee Director after the IPO Date automatically shall, upon the date of
his or her re-election or re-appointment, be granted an Option to purchase 5,000
shares of Common Stock on the terms and conditions set forth herein. Directors
serving on the date that the Company's stockholders approve the Plan may not
receive any Options under this subsection.

7. OPTION PROVISIONS.

      Each Option Agreement shall be in such form and shall contain such terms
and conditions as required by the Plan. Each Option Agreement shall contain such
additional terms and conditions, not inconsistent with the Plan, as the Board
deems appropriate. Each Option shall include (through incorporation of
provisions hereof by reference in the Option Agreement 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 the Option is granted under 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 the Common Stock acquired
      on exercise of 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) if at the time of exercise the Common Stock is publicly
            traded and quoted regularly in The Wall Street Journal, by delivery
            of shares of Common Stock that the Optionholder either has held for
            the period required
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            to avoid a charge to the Company's reported earnings (generally six
            months) or 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 these 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 the tender would violate the provisions of any law,
            regulation or agreement restricting the redemption of the Company's
            stock; and

                  (iii) if at the time of exercise the Common Stock is publicly
            traded and quoted regularly in The Wall Street Journal, under 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 irrevocable instructions to pay the aggregate exercise
            price to the Company from the sales proceeds.

            (d) TRANSFERABILITY. Except as expressly provided otherwise in this
      paragraph, the Options are not transferable. An Option is transferable:

                  (i)   by will or by applicable laws of descent and
                        distribution;

                  (ii)  by instrument to an inter vivos or testamentary trust,
                        in a form accepted by the Company, in which the Option
                        is to be passed to a member of the Optionholders'
                        "immediate family" as this term is defined in 17 C.F.R.
                        240.16a-1(e), upon the death of the trustor (settlor);
                        or

                  (iii) by gift, in a form accepted by the Company, to a member
                        of the Optionholder's immediate family.

      An Option shall be exercisable during the lifetime of the Optionholder
      only by the Optionholder and a permitted transferee as provided herein.
      However, 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, may thereafter
      exercise the Option for the benefit of the Optionholder's permitted
      beneficiary.

            (e) EXERCISE SCHEDULE. The Option shall be exercisable as the shares
      of Common Stock subject to the Option vest.
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            (f) VESTING SCHEDULE. The Options granted under this Plan, whether
      under an Initial Grant or a Subsequent Grant, shall provide for vesting of
      1/36th of the shares of Common Stock subject to the Option each month
      after the date of the grant of the Options over 3 years.

            (g) TERMINATION OF CONTINUOUS SERVICE. If 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 may 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.

            (h) 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 expiration of a period of three
      (3) months following the date on which the exercise of the Option would no
      longer be in violation of such registration requirements after the
      termination of the Optionholder's Continuous Service.

            (i) 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 twelve (12) months following the termination or (ii) the
      expiration of the term of the Option as set forth in the Option Agreement.
      If, after termination as a result of the Option holder's disability, the
      Optionholder does not exercise his or her Option within the time specified
      herein, the Option shall terminate.

            (j) DEATH OF OPTIONHOLDER. If (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 for the benefit of the Optionholder's
      permitted
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      beneficiary, but only within the period ending on the earlier of (i) the
      date eighteen (18) months following the date of death or (ii) the
      expiration of the term of the 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 reserve at all times the number of shares of Common Stock required to
satisfy the 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 an Option. If, after reasonable
efforts, the Company cannot obtain from any such regulatory commission or agency
the authority that 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 the Options
unless and until the 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 until the Optionholder has satisfied all requirements
for exercise of the Option under 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 under the terms of the Consultant's agreement with the Company or an
Affiliate or (iii) the service of a Director under 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.
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      (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 these requirements, shall be inoperative if (i)
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 (ii) as to any particular requirement, a
determination is made by counsel for the Company that the 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 the Company 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 Company's obligation to issue shares of
Common Stock upon exercise of an Option is expressly conditioned on the
Optionholder satisfying any federal, state or local tax withholding obligations
relating thereto. The Optionholder may satisfy this withholding obligation 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
these 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. Shares of Common Stock delivered to satisfy withholding obligations under
this section shall be determined in a manner similar to that provided in section
7(c) above.

II. 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 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
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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 these 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) DISSOLUTION OR LIQUIDATION. If the Company dissolves or liquidates,
then all outstanding Options shall terminate immediately before this event.

      (c) CHANGE IN CONTROL. 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 any surviving corporation or acquiring
corporation may assume any Options outstanding under the Plan or may substitute
similar Options (including an option to acquire the same consideration paid to
the stockholders in the transaction described in this subsection 11(c)) for
those outstanding under the Plan. In the event no surviving corporation or
acquiring corporation assumes the Options or substitutes similar Options for
those outstanding under the Plan, then (i) with respect to Options held by
Optionholders whose Continuous Service has not terminated, the vesting of the
Options (and the time during which the Options may be exercised) shall be
accelerated in full when the Board approves the event, and the Options shall
terminate if not exercised at or prior to the event; and (ii) with respect to
any other Options outstanding under the Plan, such Options shall terminate if
not exercised at or prior to the event.

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.

      (b) STOCKHOLDER APPROVAL. The Board may, in its sole discretion, submit
for stockholder approval any other amendment to the Plan not otherwise requiring
stockholder approval to satisfy the requirements of Rule 16b-3 or any NASDAQ or
securities exchange listing requirements.

      (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
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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 unless (i) the Company requests the consent of the Optionholder and (ii)
the Optionholder consents in writing.

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 Texas, without regard to
conflict of laws rules.