Document:

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                                                                    EXHIBIT 10.4

                       NONQUALIFIED STOCK OPTION AGREEMENT

GRANTED TO:                        Russell A. Wiseman

DATE OF GRANT:                     May 10, 2001

GRANTED PURSUANT TO:               Nucentrix Broadband Networks, Inc.
                                   First Amended and Restated 1999 Share
                                   Incentive Plan, as amended

NUMBER OF UNDERLYING               20,000 shares
SHARES OF COMMON
STOCK:

EXERCISE PRICE:                    $9.68 per share

VESTING SCHEDULE:                  See Paragraph 4 below

         1. This Nonqualified Stock Option Agreement (the "Agreement") is made
and entered into as of May 10, 2001 (the "Date of Grant"), between Nucentrix
Broadband Networks, Inc., a Delaware corporation (the "Company"), and Russell A.
Wiseman ("Employee"). It is the intent of the Company and Employee that the
Option (as defined in Paragraph 2 below) will not qualify as an "incentive stock
option" under Section 422 of the Internal Revenue Code of 1986, as amended from
time to time (the "Code").

         2. Employee is granted an option (the "Option") by the Compensation
Committee of the Company's Board of Directors (the "Committee") to purchase
20,000 shares of common stock of the Company, par value $.001 ("Common Stock")
pursuant to the Company's First Amended and Restated 1999 Share Incentive Plan,
as amended (the "Plan"). Capitalized terms not defined herein shall have the
meanings ascribed thereto in the Plan. The Option granted hereunder is a matter
of separate inducement and is not in lieu of salary or other compensation for
Employee's services.

         3. The Option's exercise price is $9.68 per share, such exercise price
being in the judgment of the Committee not less than one hundred percent (100%)
of the Fair Market Value of a share of Common Stock on the Date of Grant.

         4. Subject to Paragraphs 5, 6 and 7 below, 20% of the Option will
automatically vest and become exercisable on each of the first five
anniversaries of the Date of Grant.

         Notwithstanding anything herein to the contrary, if the Employee is
employed by the Company on the date which is 30 days immediately prior to the
Expiration Date (such date referred to herein as the "Final Vesting Date"), the
unvested portion, if any, of the Option will immediately vest and become
exercisable on such date.

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         5. Subject to Paragraphs 6 and 7 below, the unexercised portion of the
Option, unless sooner terminated, shall expire seven years after the Date of
Grant (the "Expiration Date") and, notwithstanding anything contained herein to
the contrary, no portion of the Option may be exercised after the Expiration
Date.

         6. If prior to the Expiration Date, Employee's employment with the
Company or any subsidiary corporation terminates, the Option will terminate on
the applicable date as described below, provided, however, that none of the
events described below shall extend the period of exercisability beyond the
Expiration Date:

            (a) If the employment of Employee is terminated by reason of
Employee's death while in the employ of the Company or any subsidiary
corporation, the Option shall immediately become fully exercisable and remain
exercisable for twelve (12) months after Employee's death and shall be
exercisable by the executor or administrator of the estate of the deceased
Employee or the person or persons to whom the deceased Employee's rights under
the Option shall pass by will or the laws of descent or distribution;

            (b) If the employment of Employee is terminated by the Company or
any subsidiary corporation for reason of Employee's "Permanent Disability" (as
defined below), the Option shall immediately become fully exercisable on the
date of such termination and shall remain exercisable for six (6) months after
such date; provided, however, that if Employee dies during the six month period
following such date and Employee has not exercised the Option, the Option shall
remain exercisable for an additional twelve (12) months after Employee's death
and shall be exercisable by the executor or administrator of the estate of the
deceased Employee or the person or persons to whom the deceased Employee's
rights under the Option shall pass by will or the laws of descent or
distribution;

            (c) If the employment of Employee is terminated by the Company or
any subsidiary corporation for "Cause" (as defined below), the Option shall, to
the extent not previously exercised, immediately become null and void on the
date of such termination;

            (d) If the employment of Employee is terminated by the Company or
any subsidiary corporation other than (X) for "Cause", (Y) for reason of
Employee's death or "Permanent Disability," the Option, to the extent vested and
not previously exercised, shall immediately become fully exercisable on the date
of such termination and shall remain exercisable for thirty (30) days after such
date and the unvested portion of the Option shall be canceled;

            (e) If the employment of Employee is terminated by the Employee
prior to the Final Vesting Date, the unvested portion of the Option shall
immediately become null and void on the date of such termination and the vested
portion of the Option shall, to the extent not previously exercised, remain
exercisable for thirty (30) days after the date of such termination; or

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            (f) If the employment of Employee is terminated by the Employee on
or after the Final Vesting Date, the Option shall, to the extent not previously
exercised, remain exercisable for thirty (30) days after the date of such
termination.

            For purposes of this Agreement, the terms "Permanent Disability" and
"Cause" shall have the meanings ascribed to such terms in Annex A attached
hereto.

         7. Upon the occurrence of a "Change in Control" (as defined in the
Plan), the Option shall immediately become fully exercisable and shall terminate
thirty (30) days after the occurrence of the Change in Control. Upon such
termination, Employee shall receive, with respect to the unexercised portion of
the Option, an amount in cash, in one or more kinds of property (including the
property, if any, payable in the transaction) or in a combination thereof, as
the Committee, in its discretion, shall determine, equal to the product of (X)
the amount, if any, by which the Fair Market Value of a share of Common Stock
immediately prior to the occurrence of such Change in Control exceeds the
exercise price per share specified in Paragraph 3 hereof and (Y) the number of
shares with respect to which the Option remained exercisable on the date of such
termination; provided, however, that the apportionment and kind of property, if
any, to be received by the Employee shall not differ in any material respect
from the property to be received by the holders of Common Stock.

         8. Employee may exercise the Option regardless of whether any other
option that Employee has been granted by the Company remains unexercised. In no
event may Employee exercise the Option for a fraction of a share or for less
than 100 shares unless such number is the remaining balance for which the Option
is then exercisable.

         9. The Option's exercise price shall be paid by Employee on the date
the Option is exercised, in full in cash or, in the sole discretion of the
Committee, in shares of Common Stock or any other method that the Committee
shall prescribe, including, without limitation, by the withholding of shares or
the delivery of an executed promissory note to the Company on such terms and
conditions as the Committee shall determine in its sole discretion.

         10. The Company or any subsidiary corporation may withhold from sums
due or to become due to Employee from the Company or any subsidiary corporation
an amount necessary to satisfy its obligation to withhold taxes incurred by
reason of the issuance or disposition of shares pursuant to the Option, or may
require Employee to reimburse the Company or any subsidiary corporation in such
amount. The exercise of the Option shall not be effective until the withholding
tax liability associated with the exercise of the Option has been satisfied.

         11. Employee shall not have any of the rights of a stockholder with
respect to the shares of Common Stock underlying the Option while the Option is
unexercised.

         12. Any exercise of this Option shall be in writing addressed to the
Corporate Secretary of the Company at the principal place of business of the
Company, specifying

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the Option being exercised and the number of shares to be purchased, accompanied
by payment therefor.

         13. This Option shall not be transferable otherwise than by will or the
laws of descent and distribution, and shall be exercisable, during Employee's
lifetime, only by Employee. Notwithstanding the foregoing, but subject to the
approval of the form of the transfer by the Committee which approval shall not
be unreasonably withheld, this Option may be transferred by Employee solely to
Employee's spouse, siblings, parents, children and grandchildren or trusts for
the benefit of such persons, subject to any restriction included in this
Agreement.

         14. If the Company, in its sole discretion, shall determine that it is
necessary, to comply with applicable securities laws, the certificate or
certificates representing the shares purchased pursuant to the exercise of the
Option shall bear an appropriate legend in form and substance, as determined by
the Company, giving notice of applicable restrictions on transfer under or in
respect of such laws.

         15. The Company agrees that at the time of exercise of the Option it
will use reasonable efforts in good faith to have an effective Registration
Statement on Form S-8 under the Securities Act of 1933, as amended (the "Act"),
which includes a prospectus that is current with respect to the shares subject
to the Option. Employee covenants and agrees with the Company that if, at the
time of exercise of the Option, there does not exist a Registration Statement on
an appropriate form under the Act, which Registration Statement shall have
become effective and shall include a prospectus that is current with respect to
the shares subject to the Option, (i) that he or she is purchasing the shares
for his or her own account and not with a view to the resale or distribution
thereof, (ii) that any subsequent offer for sale or sale of any such shares
shall be made either pursuant to (x) a Registration Statement on an appropriate
form under the Act, which Registration Statement shall have become effective and
shall be current with respect to the shares being offered and sold, or (y) a
specific exemption from the registration requirements of the Act and applicable
state securities laws, but in claiming such exemption, Employee shall, prior to
any offer for sale or sale of such shares, obtain a favorable written opinion
from counsel for or approved by the Company as to the applicability of such
exemption and (iii) that Employee agrees that the certificates evidencing such
shares shall bear a legend to the effect of the foregoing.

         16. This Agreement is subject to all terms, conditions, limitations and
restrictions contained in the Plan, which shall be controlling in the event of
any conflicting or inconsistent provisions.

         17. This Agreement is not a contract of employment and the terms of
Employee's employment shall not be affected hereby or by any agreement referred
to herein except to the extent specifically so provided herein or therein.
Nothing herein shall be construed to impose any obligation on the Company or any
subsidiary corporation to continue Employee's employment, and it shall not
impose any obligation on Employee's part to remain in the employ of the Company
or any subsidiary corporation.

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         18. Employee acknowledges and agrees that neither the Company, its
stockholders nor its directors and officers, has any duty or obligation to
disclose to the Employee any material information regarding the business of the
Company or any subsidiary corporation or affecting the value of the Common Stock
before or at the time of a termination of the employment of Employee by the
Company or any subsidiary corporation, including, without limitation, any
information concerning plans for the Company or any subsidiary corporation to
make a public offering of its securities or to be acquired by or merged with or
into another firm or entity.

            IN WITNESS WHEREOF, the undersigned have executed this Agreement as
of the date first written above.

                                    NUCENTRIX BROADBAND NETWORKS, INC.

                                    By: /s/ Carroll D. McHenry
                                        ------------------------------------
                                        Carroll D. McHenry
                                        Chairman and Chief Executive Officer

ACCEPTED: /s/ Russell A. Wiseman
          ---------------------------
          Russell A. Wiseman

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                                     ANNEX A
                     TO NONQUALIFIED STOCK OPTION AGREEMENT
            BETWEEN NUCENTRIX BROADBAND NETWORKS, INC. ("NUCENTRIX")
                             AND RUSSELL A. WISEMAN

"Cause" shall mean a finding by a majority of the directors of Nucentrix that
you have:

(1)      acted with gross negligence or willful misconduct in connection with
         the performance of your duties as an officer of Nucentrix;

(2)      engaged in a material act of insubordination or of common law fraud
         against Nucentrix or its employees;

(3)      acted against the best interests of Nucentrix in a manner that has or
         could have a material adverse affect on the financial condition of
         Nucentrix;

(4)      been convicted of a crime or pleaded nolo contendere (other than minor
         infractions and traffic violations);

(5)      materially violated your duty of loyalty to Nucentrix which results or
         may reasonably be expected to result in material injury to Nucentrix or
         any subsidiary; or

(6)      engaged in chronic alcohol or drug abuse.

"Permanent Disability" shall mean any physical or mental disability which
renders you unable to perform the essential functions of your job as an employee
of Nucentrix on a full-time basis with or without reasonable accommodation for
180 calendar days whether or not consecutive, within any period of 12
consecutive months.

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                                                                    EXHIBIT 10.1

                               ILEX ONCOLOGY, INC.

                             1995 STOCK OPTION PLAN

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                                TABLE OF CONTENTS

<Table>
<Caption>
<S>                                                                                                          <C>
1.   PURPOSES OF THE PLAN...................................................................................  1

2.   DEFINITIONS............................................................................................  1

3.   SCOPE OF THE PLAN......................................................................................  3

4.   ADMINISTRATION.........................................................................................  3

5.   STOCK SUBJECT TO THE PROGRAM; ADJUSTMENTS UPON CHANGES IN CAPITALIZATION...............................  4

6.   STOCK OPTIONS..........................................................................................  5

7.   GENERAL PROVISIONS.....................................................................................  9

8.   COMPLIANCE WITH OTHER LAWS AND REGULATIONS............................................................. 10

9.   EFFECTIVE DATE......................................................................................... 11

10.  AMENDMENT OR TERMINATION OF PROGRAM.................................................................... 11

11.  APPLICABLE LAW......................................................................................... 11
</Table>

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                              AMENDED AND RESTATED
                               ILEX ONCOLOGY, INC.
                             1995 STOCK OPTION PLAN

1. PURPOSES OF THE PLAN

         1.1. The purposes of the ILEX Oncology, Inc. 1995 Stock Option Plan are
(a) to assist ILEX Oncology, Inc. in attracting and retaining in the employ of
the Company and any Subsidiaries individuals of outstanding competence, and (b)
to provide performance incentives for officers, executives, key employees of and
advisors and independent consultants to the Company and any Subsidiaries.

2. DEFINITIONS

         Unless otherwise required by the context, the terms used in this Plan
shall have the meanings indicated in this Section 2. Except where context
indicates otherwise, the use of the masculine shall include the feminine, and
the use of the singular shall include the plural.

         "Beneficiary": As applied to a participant in the Plan, a person or
entity (including a trust or the estate of the participant) designated in
writing by the participant on such forms as the Committee may prescribe to whom
an Option may pass in the event of the death of the participant. If, at the
death of a participant, there shall not be any living person or entity in
existence so designated, the term "Beneficiary" shall mean the legal
representative of the participant's estate.

         "Board or Board of Directors": The Board of Directors of the Company.

         "Committee": The Option Committee of the Board of Directors or such
other committee as may be designated by the Board of Directors under Section 4.1
to administer the Plan.

         "Common Stock": The common stock of the Company, $.01 par value, or
such other class of shares or other securities as may be applicable in
accordance with Sections 5.1 and 5.2.

         "Company": ILEX Oncology, Inc., a Delaware corporation, its successors
and assigns.

         "Consultant": A non-employee director on the Company's Board of
Directors, or an advisor or independent consultant to the Company who, in the
opinion of the Committee, is in a position to make significant contributions to
the Company or a Subsidiary.

         "Incentive Stock Option": A form of stock option which, by specific
provision of the Internal Revenue Code of 1986, as amended, is not subject to
federal income tax at the time of its grant or exercise and is issuable only to
employees of the corporation granting the option or a parent or subsidiary of
such corporation.

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         "Key Employee": An employee of the Company or of a Subsidiary regularly
employed on a full-time basis, including an officer or director if he is such an
employee, who, in the opinion of the Committee, is in a position to make
significant contributions to the Company or a Subsidiary.

         "Market Value": As applied to a specific date and unless otherwise
specifically defined in the text of the Plan, (i) the closing sale price of the
Common Stock for such date as reported on the National Association of Securities
Dealers Automated Quotation ("NASDAQ") system (or, if no such sales were
reported for such date, on the next preceding date for which such sales were
reported), or (ii) if the price of Common Stock is not reported on the NASDAQ
system or any other national exchange, the fair market value as determined in
good faith by the Committee.

         "Option" or "Stock Option": An option to purchase shares of Common
Stock granted under Section 6.1.

         "Optionee": A Key Employee or Consultant who has received an Option or
Options under the Plan.

         "Permanent Disability": The permanent incapacity of a participant in
the Plan to perform the usual duties of his employment by reason of physical or
mental impairment. For this purpose, "Permanent Disability" shall be deemed to
exist if Optionee is unable by reason of material physical or mental impairment
to perform the duties of his regular position with the Company and is not
expected to recover from his disability within a period of six months from the
commencement of the disability. If at any time Optionee has claimed to be
permanently disabled, a physician acceptable to both Optionee and the Committee
(which acceptances shall not be unreasonably withheld) shall be retained by the
Committee and shall examine Optionee. Optionee shall cooperate fully with the
physician. If the physician determines that Optionee is permanently disabled,
the physician shall deliver to the Committee a certificate certifying both that
Optionee is permanently disabled and the date upon which the condition of
permanent disability commenced. The determination of the physician shall be
conclusive. For purposes of Options that are Incentive Stock Options, Permanent
Disability shall be interpreted in a manner that is consistent with Internal
Revenue Code Section 22(e)(3).

         "Plan": The ILEX Oncology, Inc. 1995 Stock Option Plan, as amended from
time to time.

         "Restricted Stock": Shares of Common Stock issued or transferred
subject to restrictions precluding a sale or other disposition for a period of
time (other than as specifically may be permitted) and requiring, as a condition
to retention, compliance with any other terms and conditions that may be imposed
by the Committee.

         "Retirement": The termination of a participant's employment with the
Company and its Subsidiaries due to and consistent with the retirement policies
of the Company and its Subsidiaries.

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         "Rule 16b-3": As applied on a specific date, Rule 16b-3 of the General
Rules and Regulations under the Securities Exchange Act of 1934 as then in
effect or any other provision that may have replaced such Rule and be then in
effect.

         "Subsidiary": Any corporation or other form of business association of
which shares (or other ownership interests) having more than 50% of the voting
power are owned or controlled, directly or indirectly, by the Company.

         "Supplement": Rules of general application consistent with the Plan
adopted by the Committee as a supplement thereto for the administration or
implementation of the Plan or a portion thereof.

3. SCOPE OF THE PLAN

         The Plan shall apply to the Company and to any Subsidiaries which have
not been specifically excluded by the Board of Directors.

4. ADMINISTRATION

         4.1. The Plan shall be administered by a committee of two or more
persons selected by the Board of Directors from its own membership who are not
employees of the Company, which shall be the Option Committee of the Board of
Directors unless another committee of the Board shall be designated by the
Board.

         4.2. The Committee shall have full power to interpret and administer
the Plan and full authority to act in determining who shall be participants in
the Plan, the number of Options to be granted to each participant, and the
conditions, form, manner, time and terms of payment under such Options. The
interpretation by the Committee of the terms and provisions of the Plan and the
administration thereof, and all action taken by the Committee, shall be final,
binding and conclusive on the Company, its stockholders, Subsidiaries, all
participants and employees, and upon their respective Beneficiaries, successors
and assigns, and upon all other persons claiming under or through any of them.

         4.3. The Committee may adopt such rules, regulations and Supplements,
not inconsistent with the provisions of the Plan, as it deems necessary (a) to
determine participation in the Plan, the amount to be granted to each
participant and the conditions, form, manner, time and terms of payment under
such Options and (b) to administer the Plan, and may amend or revoke any such
rule, regulation or Supplement.

         4.4. No member or former member of the Committee or of the Company's
Board of Directors shall be liable for any action or determination made in good
faith with respect to the Plan or any Option granted hereunder. To the maximum
extent permitted by applicable law, each member or former member of the
Committee or of the Company's Board of Directors shall be indemnified and held
harmless by the Company against any cost or expense (including reasonable fees
and expenses of counsel) or liability (including any sum paid in settlement of a
claim with the approval of the Company), arising out of any act or omission to
act in connection

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with the Plan, unless arising out of such member's or former member's own fraud
or bad faith. Such indemnification shall be in addition to any rights of
indemnification the members or former members may have as directors or under the
by-laws of the Company.

5. STOCK SUBJECT TO THE PROGRAM; ADJUSTMENTS UPON CHANGES IN CAPITALIZATION

         5.1. The aggregate number of shares of Common Stock which may be issued
or transferred under the Plan shall not exceed 1,800,000, subject to Sections
5.2 and 6.2(l). Such shares may be authorized but unissued shares of Common
Stock, shares of treasury stock or shares purchased for the Plan under Section
7.5.

         5.2. The existence of outstanding Options shall not affect in any way
the right or power of the Company or its stockholders to make or authorize any
or all adjustments, recapitalizations, reorganizations or other changes in the
Company's capital structure or its business, or any merger or consolidation of
the Company, or any issue of bonds, debentures, preferred or prior preference
stock ahead of or affecting the Common Stock or the rights of the Common Stock,
or the dissolution or liquidation of the Company, or any sale or transfer of all
or any part of its assets or business, or any other corporate act or proceeding,
whether of a similar character or otherwise.

         If the Company shall effect a subdivision or consolidation of shares or
other capital readjustment, the payment of a stock dividend, or other increase
or reduction of the number of shares of the Common Stock outstanding, without
receiving compensation for it in money, services or property, then (a) the
number, class and per share price of shares of stock subject to outstanding
Options under this Plan shall be appropriately adjusted in a manner as to
entitle an optionee to receive upon exercise of an Option, for the same
aggregate cash consideration, the same total number and class or classes of
shares as he would have received had he exercised his Option in full immediately
prior to the event requiring the adjustment; and (b) the number and class of
shares then reserved for issuance under this Plan shall be adjusted by
substituting for the total number and class of shares of stock then reserved for
the number and class or classes of shares of stock that would have been received
by the owner of an equal number of outstanding shares of Common Stock as the
result of the event requiring the adjustment.

         If the Company merges or consolidates with another corporation, whether
or not the Company is a surviving corporation, or if the Company is liquidated
or sells or otherwise disposes of substantially all its assets while unexercised
Options remain outstanding under the Plan, (a) subject to the provisions of
clause (c) below, after the effective date of the merger, consolidation,
liquidation, sale or other disposition, as the case may be, each holder of an
outstanding Option shall be entitled, upon exercise of an Option, to receive, in
lieu of shares of Common Stock, the number and class or classes of shares of
stock or other securities or property to which the holder would have been
entitled if, immediately prior to the merger, consolidation, liquidation, sale
or other disposition, the holder had been the holder of record of a number of
shares of Common Stock equal to the number of shares as to which the Option may
be exercised.

         Except as expressly provided before in this Plan, the issue by the
Company of shares of stock of any class, or securities convertible into shares
of stock of any class, for cash or property, or for labor or services either
upon direct sale or upon the exercise of rights or warrants to

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subscribe for shares, or upon conversion of shares or obligations of the Company
convertible into shares or other securities, shall not affect, and no adjustment
by reason of it shall be made with respect to, the number or price of shares of
Common Stock then subject to outstanding Options.

6. STOCK OPTIONS

         6.1.     GRANTS OF OPTIONS.

         (a)      The form or forms of Options and the number of shares of
                  Common Stock to be made subject to such Options shall be
                  determined by the Committee. Any or all Options granted to Key
                  Employees under the Plan may be in the form of Incentive Stock
                  Options, as determined by the Committee. Incentive Stock
                  Options may be granted by the Committee in substitution for
                  any Stock Option heretofore or hereafter granted to Key
                  Employees under the Plan or under any prior stock option plans
                  of the Company, and such substitution shall not be deemed the
                  grant of a new or additional Option for any purpose under the
                  Plan or otherwise, to the extent permitted by applicable law.

         (b)      Subject to the adjustment provisions of Section 5.2, the
                  maximum number of shares of Common Stock which may be issued
                  or transferred to a participant subject to Stock Options in
                  any single year shall not exceed 100,000.

         (c)      Notwithstanding anything in the Plan to the contrary, the
                  aggregate Market Value (determined on the date the Option is
                  granted) of the Common Stock for which any Key Employee may be
                  granted Incentive Stock Options in the calendar year in which
                  such Options are first exercisable (under all plans of the
                  Company or any Subsidiary which provide for the granting of
                  Incentive Stock Options) shall not exceed $100,000.
                  Consultants may not be granted Incentive Stock Options.

         6.2.     OPTION PROVISIONS. Options shall be subject to the following
                  provisions:

         (a)      Options may be granted only to Key Employees and Consultants
                  selected by the Committee.

         (b)      The Option price per share of Common Stock shall be determined
                  by the Committee, but shall not be less than 100% of the
                  Market Value thereof on the date the Option is granted.

         (c)      The expiration date of each Option shall be established by the
                  Committee at the time the Option is granted, but such date
                  shall not be later than 10 years from the date the Option is
                  granted. Except as required with respect to Incentive Stock
                  Options under Section 422 of the Internal Revenue Code of
                  1986, as amended, the Committee may extend the term of an
                  Option which has a term of less than 10 years for a period
                  ending not later than 10 years from the date of the Option
                  grant and such extension shall not be deemed the grant of a
                  new or additional Option for any purpose under the Plan or
                  otherwise. The extension of the term of an

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                  Option shall be subject to the consent of the holder of the
                  Option and may be made at any time prior to the expiration of
                  the Option. Incentive Stock Options may not be granted more
                  than 10 years after the Plan is adopted by the stockholders of
                  the Company.

         (d)      Options may be exercised as to all or any portion of the
                  shares of Common Stock subject to the Option while the
                  original Optionee has a relationship with the Company which
                  confers eligibility to be granted Options, but not later than
                  the expiration date specified in such Option.

         (e)      Options granted to a Key Employee shall not be affected by any
                  change in the nature of the Key Employee's employment so long
                  as he continues to be employed by the Company or a Subsidiary.
                  Approved leaves of absence shall not be considered a
                  termination or interruption of full-time employment for any
                  purpose of the Plan.

         (f)      Each Option shall terminate if and when the Optionee shall
                  cease to be an employee of or advisor or consultant to the
                  Company or its Subsidiaries, except as follows (subject to the
                  provisions of the Internal Revenue Code and applicable
                  regulations of the U.S. Treasury Department concerning
                  Incentive Stock Options):

                  (i)      If an Optionee dies while an employee of the Company
                           or a Subsidiary, his Option may be exercised to the
                           extent that the Optionee could have done so at the
                           date of his death by his Beneficiary, at any time, or
                           from time to time, within one year after the date of
                           the Optionee's death but not later than the
                           expiration date specified in such Option.

                  (ii)     If an Optionee's employment by the Company or a
                           Subsidiary shall terminate because of Permanent
                           Disability, such employee may exercise his Option, to
                           the extent that he could have done so at the date of
                           his termination of employment, at any time, or from
                           time to time, within one year of such termination but
                           not later than the expiration date specified in such
                           Option.

                  (iii)    If an Optionee's employment by the Company or a
                           Subsidiary shall terminate due to Retirement, the
                           Optionee may exercise any Option to the extent that
                           he could have done so at the date of his termination
                           of employment, at any time, or from time to time,
                           within one year of such Retirement (three months in
                           the case of an Incentive Stock Option) but not later
                           than the expiration date specified in such Option.

                  (iv)     Except as provided in the following provisions of
                           this Section 6.2(f), if the Optionee's employment by
                           the Company or a Subsidiary shall terminate for any
                           reason other than death, Permanent Disability or
                           Retirement, he may exercise his Option, to the extent
                           that he could have done so at the

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                           date of his termination of employment, at any time,
                           or from time to time, within three months of the date
                           of termination of his employment but not later than
                           the expiration date specified in such Option.

                  (v)      Notwithstanding anything in the Plan to the contrary,
                           if an Optionee's employment is terminated for cause,
                           his ability to exercise such Option shall terminate
                           on the date of his termination of employment. For
                           this purpose, termination for "cause" shall include
                           termination for reason of (i) Optionee's conviction
                           for, or plea of nolo contendere to, a felony, (ii)
                           Optionee's commission of an act involving
                           self-dealing, fraud or personal profit materially
                           injurious to the Company or a Subsidiary, (iii)
                           Optionee's commission of an act of willful misconduct
                           or gross negligence in the conduct of his employment
                           duties to the Company or a Subsidiary, (iv) habitual
                           absenteeism or tardiness on the part of Optionee with
                           respect to his employment with the Company or a
                           Subsidiary, (v) Optionee's breach or violation of any
                           material internal policies or rules of the Company or
                           a Subsidiary concerning the purchase and sale of that
                           entity's common stock or other securities by
                           employees of the Company or a Subsidiary, and (vi)
                           Optionee's breach of any material provision of any
                           written employment agreement between Optionee and the
                           Company or a Subsidiary. The Committee shall
                           determine in its sole discretion whether a
                           termination was made for cause.

                  (vi)     Notwithstanding anything in the Plan to the contrary,
                           the Committee may at any time with the consent of a
                           majority of the disinterested directors of the
                           Company's Board of Directors terminate an Option if
                           it shall, in the reasonable exercise of its judgment,
                           find that the Optionee has disclosed without the
                           written consent of an authorized officer of the
                           Company, to any person not employed by or engaged to
                           render services to the Company or a Subsidiary, any
                           material confidential information of the Company or a
                           Subsidiary or has engaged in material competition
                           with the Company or any Subsidiary or in any
                           activities otherwise contrary to the best interests
                           of the Company or a Subsidiary. The right to exercise
                           the Option has been granted, and the compensation to
                           be realized in the event of exercise has been
                           provided, upon the express understanding that the
                           Optionee shall refrain from engaging in any
                           activities contrary to the best interests of the
                           Company.

         (g)      If any Optionee is not an employee of the Company or a
                  Subsidiary, but rather is a Consultant to the Company or a
                  Subsidiary, the following provisions shall apply as if the
                  Optionee were an employee of the Company or a Subsidiary:

                  (i)      Section 6.2(f)(i) shall apply if the Consultant
                           relationship terminates because of the Optionee's
                           death.

                                       7
<PAGE>   10

                  (ii)     Section 6.2(f)(ii) shall apply if the Consultant
                           relationship terminates because of the Optionee's
                           Permanent Disability.

                  (iii)    Section 6.2(f)(iii) shall apply if the Consultant
                           relationship terminates because of the Optionee's
                           retirement.

                  (iv)     Section 6.2(f)(iv) shall apply if the Consultant
                           relationship terminates for any other reason than the
                           Optionee's death, Permanent Disability or retirement.

                  (v)      Notwithstanding paragraphs (f)(i) through (f)(iv),
                           above, Section 6.2(f)(v) shall apply if the
                           Consultant relationship is terminated by the Company
                           or a Subsidiary for cause.

                  (vi)     Section 6.2(f)(vi) shall apply as written.

         (h)      Subject to the provisions of Sections 6.2(c), (d), (e), (f)
                  and (g) and of the Option agreement pursuant to which an
                  Option is granted, Options may be exercised, in whole or in
                  part, at any time during the term of the Option.

         (i)      An Option shall be considered exercised under the Plan on the
                  date written notice is mailed (postage prepaid) or delivered
                  to the Secretary of the Company advising of the exercise of a
                  particular Option and transmitting payment of the Option price
                  for the shares involved, but this provision shall not preclude
                  exercise of an Option by any other proper legal method.

         (j)      Options are not transferable other than by will or by the laws
                  of descent and distribution, and during a participant's
                  lifetime are exercisable only by the Optionee or by his or her
                  guardian or legal representative.

         (k)      The Committee may place such conditions and restrictions on
                  the exercise of Options and on the transferability of shares
                  of Common Stock received upon exercise of an Option, in
                  addition to those contained herein, as it shall deem
                  appropriate and, without limiting the generality of the
                  foregoing, may provide in the Option grant that shares of
                  Common Stock issued or transferred upon exercise of the Option
                  shall be shares of Restricted Stock subject to forfeiture upon
                  failure to comply with such conditions and restrictions.

         (l)      Following the death of a participant, and upon the request of
                  the Beneficiary, the Company may at its election, (i) at any
                  time while the Option may be exercised, purchase the Option at
                  a price equal to the difference between the Market Value, on
                  the date such request is mailed (postage prepaid) or delivered
                  to the Secretary of the Company, of the shares of Common Stock
                  subject to exercise and the Option price of such shares of
                  Common Stock, or (ii) within thirty days following the
                  exercise of an Option, purchase the shares of Common Stock so
                  acquired at their Market Value on the date of exercise. The
                  number of shares of Common

                                       8
<PAGE>   11

                  Stock purchased by the Company shall be considered issued and
                  transferred for purposes of Sections 5.1 and 6.2(c).

         (m)      No shares of Common Stock shall be issued or transferred upon
                  exercise of an Option until full payment therefor has been
                  made. Such payment shall be made in cash. A holder of an
                  Option shall have none of the rights of a stockholder until
                  shares of Common Stock are issued or transferred as the result
                  of the exercise of such Option. The proceeds received by the
                  Company from the sale of Common Stock pursuant to the Plan
                  shall be available for general corporate purposes.

7. GENERAL PROVISIONS

         7.1. Neither the adoption of the Plan nor its operation, nor any
booklet or other document describing or referring to the Plan, or any part
thereof, (a) shall confer upon any employee any right to continue in the employ
of the Company or any Subsidiary or shall in any way affect the right and power
of the Company or any Subsidiary to dismiss or otherwise terminate the
employment of any employee at any time for any reason with or without cause, or
(b) shall confer upon any advisor or consultant to the Company or any Subsidiary
any right to continue in such capacity or shall in any way affect the right of
the Company to terminate the advisory or consulting relationship at any time for
any reason with or without cause. If the Company or any Subsidiary shall
terminate the employment or advisory or consulting relationship of a participant
for any reason, whether or not for cause, neither the Company nor such
Subsidiary shall incur any liability to the participant due to the inability of
the participant by reason of such termination to exercise thereafter any Option,
to receive any grant under the Plan or to be eligible thereafter for any grant
under the Plan.

         7.2. By accepting any benefits under the Plan, each participant and
each person claiming under or through him shall be conclusively deemed to have
indicated his acceptance and ratification of, and consent to, all provisions of
the Plan and any action or decision under the Plan by the Company, the Board of
Directors or the Committee.

         7.3. Appropriate provision shall be made for all taxes which the
Company requires to be withheld in connection with the exercise of Options,
under the laws of any governmental authority, whether Federal, state or local
and whether domestic or foreign. The Committee may in its discretion permit a
participant to elect at any time, but in no event later than six months prior to
the exercise of any Option, to have a portion of the shares subject to such
exercise withheld by the Company for the purpose of satisfying any tax
withholding under Federal, state or local tax laws.

         7.4. No rights under the Plan shall be assignable, either voluntarily
(except as may specifically be permitted for gifts of Restricted Stock), or
involuntarily by way of encumbrance, pledge, attachment, levy or charge of any
nature (except as may be required by state or federal law). Notwithstanding
anything in the Plan to the contrary, a participant may designate a Beneficiary
to receive an Option in the event of the participant's death.

                                       9
<PAGE>   12

         7.5. Nothing in the Plan shall require the Company or any Subsidiary to
segregate or set aside any funds or other property for the purpose of paying
Common Stock upon the exercise of Options. No participant, Beneficiary or other
person shall have any right, title or interest in any amount awarded under the
Plan prior to payment thereof, or in any property of the Company or its
Subsidiaries or affiliated corporations.

         7.6. It is contemplated that the Company, although under no legal
obligation to do so, may from time to time purchase shares of Common Stock for
the purpose of paying an Option, or for the purpose of replacing shares issued
or transferred in payment of an Option. All shares so purchased shall, unless
and until transferred in payment of such Option, be at all times the property of
the Company available for any corporate purpose, and no participant or employee
or Beneficiary, individually or as a group, shall have any right, title or
interest in any shares of Common Stock so purchased.

         7.7. Headings are given to the sections of the Plan solely as a
convenience to facilitate reference; neither such headings nor numbering or
paragraphing shall be deemed in any way material or relevant to the construction
of the Plan or any provision thereof.

         7.8. The use of the masculine gender shall also include within its
meaning the feminine. The use of the singular shall include within its meaning
the plural and vice versa.

8. COMPLIANCE WITH OTHER LAWS AND REGULATIONS

         The Plan, the grant and exercise of Options thereunder, and the
obligation of the Company to sell and deliver shares of Common Stock under such
Options, shall be subject to all applicable federal and state laws, rules and
regulations and to such approvals by any government or regulatory agency as may
be required. If at any time the Committee shall determine in its discretion that
the listing, registration or qualification of the shares covered by the Plan
upon any national securities exchange or under any state or federal law, or the
consent or approval of any government regulatory body, is necessary or desirable
as a condition of, or in connection with, the sale or purchase of shares under
the Plan, no shares will be delivered unless and until such listing,
registration, qualification, consent or approval shall have been effected or
obtained, or otherwise provided for, free of any conditions not acceptable to
the Committee. If shares are not required to be registered, but are exempt from
registration, upon exercising all or any portion of an Option, the Company may
require each Optionee (or any person acting under Section 6.2(f)(i)), to
represent that the shares are being acquired for investment only and not with a
view to their sale or distribution, and to make such other representations
deemed appropriate by counsel to the Company. Stock certificates evidencing
unregistered shares acquired upon exercise of Options shall bear any legend
required by applicable state securities laws and a restrictive legend
substantially as follows:

         THE SECURITIES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER THE
         SECURITIES ACT OF 1933, AS AMENDED (THE "ACT"), OR UNDER THE SECURITIES
         LAWS OF ANY STATE AND MAY NOT BE TRANSFERRED IN THE ABSENCE OF SUCH
         REGISTRATION OR AN OPINION OF COUNSEL ACCEPTABLE TO THE COMPANY THAT
         SUCH TRANSFER WILL NOT REQUIRE

                                       10
<PAGE>   13

         REGISTRATION UNDER SUCH ACT OR UNDER THE SECURITIES LAWS OF ANY STATE.

9. EFFECTIVE DATE

         The Plan shall become effective if and when, but not until, it is
approved by the stockholders of the Company.

10. AMENDMENT OR TERMINATION OF PROGRAM

         10.1. The Board of Directors may at any time and from time to time
modify, revise or amend the Plan in such respects as the Board of Directors may
deem advisable in order that the Options granted hereunder may conform to any
changes in the law or in any other respect that the Board of Directors may deem
to be in the best interests of the Company; provided, however, that without
approval by the stockholders of the Company voting the proper percentage of its
voting power, no such amendment shall make any change in the Plan for which
stockholder approval is required in order to comply with (i) Rule 16b-3, (ii)
the Internal Revenue Code of 1986, as amended, or regulatory provisions dealing
with Incentive Stock Options, (iii) any rules for listed companies promulgated
by any national stock exchange on which the Company's Common Stock is traded or
(iv) any other applicable rule or law. All Options granted under the Plan shall
be subject to the terms and provisions of the Plan and any amendment,
modification or revision of the Plan shall be deemed to amend, modify or revise
all Options outstanding under the Plan at the time of the amendment,
modification or revision.

         10.2. The Board of Directors may, by resolution adopted by a majority
of the entire Board of Directors, at any time terminate the Plan or any portion
thereof.

         10.3. No amendment or termination of the Plan or any portion thereof by
the Board of Directors or the stockholders shall, without the consent of a
participant, adversely affect any award previously made or any Option or any
other rights previously granted to him.

11. APPLICABLE LAW

         This Plan and all rights hereunder shall be governed, construed and
administered in accordance with the laws of the State of Texas.

                                       11

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