Document:

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                                                                   EXHIBIT 10.25

                             CONSULTANCY AGREEMENT

     This Consultancy Agreement ("Agreement") is made and effective this 1st day
of June, 2000, by and between Mannatech, Incorporated ("Mannatech"), a Texas
corporation whose principal place of business is 600 S. Royal Lane, Suite 200,
Coppell, Texas and Samuel L. Caster ("Caster"), who resides at 2034 W. Beltline
Road, Cedar Hill, Texas 75014.

                                  WITNESSETH:

     WHEREAS, Mannatech is in the business of operating a network marketing
company which sells a proprietary line of dietary supplements, cosmetics and
over-the-counter drugs ("Products") and which compensates its distributors
("Associates") by a defined compensation plan;

     WHEREAS, in connection with the development of its business Mannatech has
agreed to retain Caster as Global Vision Architect under terms and conditions to
be set forth herein ("Consultancy");

     WHEREAS, Mannatech intends to enter into a confidential relationship with
Caster whereby Caster will acquire an intimate knowledge of Mannatech's business
and will obtain or has obtained specialized skills. Mannatech will permit
Caster to have access to and to utilize the business goodwill, cost and pricing
information, CONFIDENTIAL INFORMATION (as defined herein) and various trade
secrets of Mannatech, including without limitation, marketing programs, business
relationships, customer lists, business plans, financial data, privileged legal
information and other compilations of information developed by  Mannatech and
essential to its business;

     WHEREAS, Caster will be a key consultant of Mannatech and Mannatech will
provide or has provided Caster with access to such CONFIDENTIAL INFORMATION and
trade secrets in reliance upon Caster entering into this Agreement; and

     WHEREAS, in conjunction with Caster's consultancy and subsequent access to
and use of the CONFIDENTIAL INFORMATION and trade secrets of Mannatech, Caster
has agreed to enter into this Agreement with Mannatech;

     NOW, THEREFORE, in consideration of the mutual covenants and agreements
contained herein and upon the terms, conditions and provisions hereinafter set
forth, Mannatech and Caster do hereby agree as follows:

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                                  ARTICLE I.
                            DUTIES AND COMPENSATION

     1. Caster is retained, commencing June 1, 2000 as Global Vision Architect
to the Company or such other comparable position as the parties shall agree. The
term of this Agreement, unless otherwise modified in writing is for a two (2)
calendar year period, ending on May 31, 2002 (the "Primary Term"). Unless this
Agreement is terminated by written notice by either party at least ninety (90)
days prior to May 31, 2002, this Agreement shall renew on June 1, 2002 for an
additional one-year period, with like automatic renewals occurring on each
subsequent anniversary date of this Agreement unless either party provides
written notice of termination to the other at least ninety (90) days prior to
such anniversary date.

     2. Caster is engaged to serve as Global Vision Architect at an annual
salary of $600,000 (Six Hundred Thousand Dollars) payable in monthly
installments on the 1st day of each month commencing on June 1, 2000. Caster's
title will be "Founder and Global Vision Architect." Caster shall report
directly to the Chief Executive Officer ("CEO"). This agreement shall not be
considered an employment agreement nor is it an offer for employment. The
parties agree that Caster is and will continue to be during the term of his
Consultancy, an independent contractor for federal income tax and all other
purposes, and will, accordingly, file, remit and pay all required amounts
attributable to such income as an independent contractor to any and all taxing
authorities, as required. Mannatech will provide a leased automobile to Caster
on comparable terms to those provided during his employment.

     3. Caster agrees to participate and engage in the following activities and
other tasks as requested by Mannatech from time-to-time:

        a.)  Act as a corporate liaison to Associates, particularly high-ranking
             Associates (the "Field");

        b.)  Communicate and promote corporate ideas and plans of Mannatech
             management team to the Field and receive from the Field and
             communicate to the Mannatech management team the Field's ideas and
             plans and criticisms of Mannatech;

        c.)  Work with other members of the Mannatech management team to assist
             in the development of sales and marketing devices;

        d.)  Appear at Mannatech-sponsored events;

        e.)  Assist with Associate-sponsored events;

        f.)  Promote Mannatech in a positive manner that is consistent with
             Caster's values of honesty and integrity;

        g.)  Provide advisement to the Mannatech management team as required
             from time-to-time; and

        h.)  Such other undertakings as the parties may hereafter agree.

     4.  Caster and Mannatech further agree that:

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        a)   Caster plans to spend a significant amount of his time promoting
             Manna Relief and that he may devote time to other businesses or
             causes from time to time during the term of his Consultancy. Caster
             agrees that during the term of his Consultancy.

             (i)   He will not promote and endorse at Mannatech business
                   functions any other organization(s) of which he is affiliated
                   other than MannaRelief without the consent of the CEO of
                   Mannatech;

             (ii)  his promotion of MannaRelief and other permitted
                   organizations shall not be presented as endorsed by or as
                   part of Mannatech;

             (iii) In written communications he will include a statement to the
                   effect that MannaRelief, or any other permitted organization,
                   as the case may be, is not a part of Mannatech and that
                   MannaRelief is open to all participants;

             (iv)  Caster will not serve as a spokesman or representative for
                   any for-profit business other than Mannatech without the
                   prior consent of the Chief Executive Officer ("CEO") of
                   Mannatech.

        b)   Caster shall not have any authority to act on behalf of Mannatech
             in the areas of negotiation or execution of any contracts or
             agreements in an attempt to bind Mannatech (or its subsidiaries)
             and will not purport to have any such authority to any third party,
             including Mannatech Associate(s). Caster will not present to third
             parties, including Mannatech Associates, any plan, program or
             position as having been approved by Mannatech unless it has been
             first proposed to the Mannatech Board of Directors and/or the CEO
             (as the case may be) and approved by the same.

        c)   During the term of his Consultancy, Caster will, for the purposes
             of fulfilling his duties under this Agreement, attend corporate and
             Associate meetings of all sorts as requested, provided he is given
             reasonable prior notice. Further, Caster shall, during the term of
             this Agreement, make such communications with corporate officers
             and employees of Mannatech as may be reasonably requested.

                                  ARTICLE II.
                 DUTIES, NON-COMPETITION and NON-SOLICITATION

     1.   Caster agrees to serve in the position of Global Vision Architect, or
such other position as the parties may hereafter agree during the term of this
Agreement, and to perform with reasonable diligence the duties and services
undertaken by Caster pursuant to such Consultancy, as well as such additional
duties and services appropriate to such Consultancy upon which the parties
mutually may agree from time-to-time or as shall be designated by the Board of
Directors.  Caster will meet with the CEO from time to time to discuss and agree
to those activities, including but not limited to these specified in Article 5,
Section 3, that Caster will

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undertake within the scope of his Consultancy. Caster also agrees that his
Consultancy is subject to the current and future policies, written directives,
and procedures maintained and established by Mannatech for its management, and
concerning which Mannatech shall inform Caster in writing. Caster shall devote
such of his time and efforts as are reasonably necessary to perform the duties
that Caster has agreed to undertake pursuant to this Agreement. Caster shall
further perform his duties in accordance with the directives of the Mannatech
Board of Directors and the CEO of Mannatech or, as the parties may agree, from
time-to-time, as the case may be. Caster may designate up to four (4) weeks
during each calendar year of the Consultancy in which he will not be available
to provide services to Mannatech.

     2.   Caster acknowledges and understands that from time to time Caster's
duties may require Caster to work on-site at a non-company location. In such
instance, Caster agrees to comply with all of the policies, procedures and
directives relevant to working at such non-company location which are generally
applicable to the Company's employees. Mannatech shall reimburse Caster for
reasonable and necessary travel and lodging expenses regarding any travel
required in connection with this Consultancy Agreement, provided that the same
are booked through the Mannatech Travel Department or otherwise approved by the
CEO of Mannatech.

     3.   Caster represents and admits that in the event of the termination of
Caster's consultancy for any reason whatsoever, Caster's experience and
capabilities are such that Caster can earn a livelihood in business engaged in
other lines and/or of a different nature, and that the enforcement of a remedy
by way of injunction will not prevent Caster from earning a livelihood.

     4.   Caster acknowledges that he will receive special knowledge and
specialized training from Mannatech, included in which is the CONFIDENTIAL
INFORMATION identified in Article III below. Caster further acknowledges that
the special knowledge and/or training provided by Mannatech and the CONFIDENTIAL
INFORMATION is valuable to Mannatech and, therefore, Mannatech's investment in
the training and the protection and maintenance of the CONFIDENTIAL INFORMATION
constitutes a legitimate interest to be protected by Mannatech by the covenant
not to compete, set forth in Article II of this Agreement.

     5.   Non-Competition.   Caster therefore agrees that for a period of one
(1) year after Caster shall cease to be a consultant of Mannatech, Caster shall
not engage in any form of business which is in competition with Mannatech,
including through the business of any person, company, firm, corporation,
partnership, association, agency, or business, and particularly through a party
known to Caster to be an independent contract sales associate and/or a customer
of Mannatech ("Subject Person") or with whom Caster had contact during, or by
reason of, Caster's consultancy to Mannatech, including any Subject Person known
to Caster prior to Caster's original consultancy to Mannatech.

     6.   Non-Solicitation.  Caster further agrees that for a period of one (1)
year after Caster shall cease to be a consultant of Mannatech, Caster will not,
either directly or indirectly, through any person, firm, association or
corporation with which Caster is now or may hereafter

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become associated with, solicit, cause, influence or induce any present or
future Subject Person of Mannatech or its affiliates to leave the employ or
business relationship with Mannatech or its affiliates to accept employment,
affiliation, associate relationship or consultancy or any other business
relationship with Caster or with such person, firm, association, or corporation
with whom Caster may then be affiliated.

     As set forth above, Caster acknowledges that the foregoing non-competition
and non-solicitation covenants are ancillary to or a part of an otherwise
enforceable agreement, such being the general agreement of this Consultancy and
its related agreements concerning confidentiality and non-disclosure of
CONFIDENTIAL INFORMATION and non-solicitation, at the time that this non-
competition covenant is made, that the limitations as to time defined herein are
reasonable and do not impose a greater restraint than is necessary to protect
the goodwill or other business interests of Mannatech, that the limitations as
to geographic area defined herein are reasonable and do not impose a greater
restraint than is necessary to protect the goodwill or other business interests
of Mannatech, and that the scope of activity to be restrained defined herein is
reasonable and does not impose a greater restraint than is necessary to protect
the good will or other business interests.

     7.   The foregoing covenants not to compete and solicit shall not be held
invalid or unenforceable because of the scope or the territory or actions
subject thereto or restricted thereby, or the period of time within which such
Agreement is operative; but an award or decree in arbitration or any judgment of
a court of competent jurisdiction, as the case may be, may define the maximum
territory and actions subject thereto and restricted by this Article II and the
period of time during which the Agreement is enforceable.  Any alleged breach of
other provisions of this Agreement asserted by Caster against Mannatech shall
not be a defense for Caster to claims arising from Mannatech's enforcement of
the provisions of this paragraph.  Should Caster violate the non-competition,
non-solicitation covenants of this Article II, then the period of time for these
covenants shall automatically be extended for the period of time from which
Caster began such violation until Caster permanently ceases such violation.

     8.   Irrespective of the term of this Agreement, and in consideration of
the promises specified in Article II of this Agreement, Mannatech agrees as
follows:

          a.   To provide specialized training as it shall deem warranted from
               time to time; and

          b.   To provide Caster with access to Mannatech's software and files,
               records, marketing procedures, processes, computer programs,
               compilations of information, records, Associate and client
               requirements, customer and associate lists and information
               pertaining to Subject Persons, pricing techniques, lists,
               formulae, lists identifying Associates, partners, potential
               investors, methods of doing business and other CONFIDENTIAL
               INFORMATION which is regularly used in the operation of the
               business

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               of Mannatech.

     9.   Caster represents and warrants that the delivery and execution of this
Agreement will not cause a breach in the terms of any existing agreement to
which he is a party nor interfere with any undertakings which he is bound to
perform or refrain from under any such agreements.

     10.  Caster shall be bound by and abide by all policies  and procedures of
Mannatech in effect during the term of his Consultancy.

     11.  Caster acknowledges and agrees that during the term of his
Consultancy he will owe a contractual duty of loyalty, fidelity, and allegiance
to Mannatech. In keeping with these duties, Caster shall make full disclosure to
Mannatech of all business opportunities pertaining to Mannatech's business and
shall not appropriate for Caster's own benefit such business opportunities.

     12.  Article II, Paragraphs 5 and 6 shall survive the execution,
performance and/or termination of this Agreement, subject to the time and scope
limitations set forth therein.

                                 ARTICLE III.
                           CONFIDENTIAL INFORMATION

     1.   Mannatech will provide or has provided Caster under his prior
employment with specialized information concerning the products and the business
operations of Mannatech. Irrespective of the term of this Agreement and in
consideration of Caster's promises specified in Article II of this Agreement,
Mannatech agrees to provide specialized training and instruction to Caster for
the job duties assigned to Caster, and agrees to provide specialized training to
Caster for such additional job duties as Mannatech and Caster may agree.

     2.   During the course of the Consultancy and training incident thereto
Caster will be or was given access to Mannatech's CONFIDENTIAL INFORMATION
concerning products and the business operations of Mannatech.

     3.   Caster acknowledges that in the further course of the Consultancy with
Mannatech, Caster will gain a close, personal and special influence with
Mannatech's customers and will be acquainted with all of Mannatech's business,
particularly Mannatech's CONFIDENTIAL INFORMATION concerning the business of
Mannatech and its affiliates.

     4.   For purposes of this Agreement "CONFIDENTIAL INFORMATION" shall mean
and include information known to Caster arising during the course of his prior
employment with Mannatech and information disclosed to Caster or known by Caster
through Caster's consultancy with Mannatech, about Mannatech's products,
processes and services, including but not limited to information concerning
inventions, trade secrets, research and development, as well as all data or
information concerning customers (including Subject Persons), customer lists

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(including downline reports and similar reports of business activities and
relevant information concerning Subject Persons), prospect lists, mailing lists,
sales leads, contracts, financial reports, sales, purchasing, price lists,
product costs, marketing programs, marketing plans, business relationships,
business methods, accounts payable, accounts receivable, accounting procedures,
control procedures and training materials, but will not include information that
is available from sources other than Mannatech without breach of any obligation
or duty owed to Mannatech.

     5.   Caster agrees to use the his reasonable efforts and will exercise
reasonable diligence to protect and safeguard the CONFIDENTIAL INFORMATION. In
this respect, Caster agrees that fulfilling the obligations of the Agreement is
part of Caster's responsibilities with Mannatech for which Caster has been
retained as a consultant and for which Caster has received consideration
therefor.

     6.   Except as may be required by Mannatech in connection with and during
the Consultancy with Mannatech, or with the express written permission of
Mannatech, Caster shall not, either during Caster's work as a consultant with
Mannatech or at any time thereafter, directly or indirectly, download, printout,
copy, remove from the premises of Mannatech, use for Caster's own benefit or for
the benefit of another person not under a confidentiality obligation, or
disclose to another, any CONFIDENTIAL INFORMATION of Mannatech.

     7.   Caster agrees that all files, memoranda, data, notes, records,
drawings, charts, graphs, analyses, letters, reports, or other documents or
similar items containing Confidential Information made or compiled by Caster,
made available to Caster or otherwise coming into Caster's possession during the
Consultancy shall remain at all times the property of Mannatech and shall be
delivered to Mannatech upon termination of the Consultancy with Mannatech or at
any other time upon request.

     8.   Further, prior to the execution of this Consultancy Agreement, Caster
was an employee of Mannatech under the terms of an Employment Agreement, dated
May 14, 1997, containing provisions regarding CONFIDENTIAL INFORMATION, similar
in scope and content to the foregoing, certain of which survived the termination
of his employment. It is the express intention and agreement of the parties that
there be no lapse in the terms and conditions under which Caster shall be bound
by to transact with regard to the CONFIDENTIAL INFORMATION of Mannatech between
the period in which the Employment Agreement was (and to certain extents
remains) in effect and under this Consultancy Agreement.

     9.   This Article III shall survive the performance and termination of this
Agreement for a period of five (5) years from the date of termination of
Caster's Consultancy.

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                                  ARTICLE IV.
                           ASSIGNMENT OF INVENTIONS

     1.   Caster agrees to promptly disclose to Mannatech and Caster hereby
assigns to Mannatech or its designee, its assigns, successors or legal
representatives, all, right, title and interest in and to any and all patents,
formulae, inventions, processes, designs, software, firmware, circuitry,
diagrams, copyrights, trade secrets, and any other proprietary information
(collectively, the "Proprietary Information") whatsoever, conceived, developed
or completed by Caster during the course of the Consultancy with Mannatech, or
using Mannatech's time, data, facilities and/or materials, provided the subject
matter of the Proprietary Information relates substantially and directly to the
business of Mannatech.

     2.   Caster agrees to assist Mannatech at any time during the Consultancy
with Mannatech, or after termination of the Consultancy by Mannatech with
reimbursement by Mannatech for all reasonable expenses incurred and with
reasonable compensation for Caster's time required if his Consultancy has
terminated, in the preparation, execution, and delivery of any assignments,
disclosures, patent applications, or papers within the scope and intent of this
Agreement reasonably required to obtain patents or copyrights in the Proprietary
Information in this or a foreign country and in connection with such other
proceedings as may be reasonably necessary to vest title to the Proprietary
Information in Mannatech, its assigns, successors, or legal representatives.

     3.   If, during Caster's Consultancy by Company, Caster creates any work of
authorship, at the request of Mannatech or in the course of the performance of
his duties under this Agreement, fixed in any tangible medium of expression,
which is the subject matter of copyright (such as videotapes, written
presentations, or acquisitions, computer programs, electronic mail, voice mail,
electronic databases, drawings, maps, architectural renditions, models, manuals,
brochures, or the like) relating to Company's business, products, or services,
whether such work is created solely by Caster or jointly with others (whether
during business hours or otherwise and whether on Company's premises or
otherwise), Company shall be deemed the author of such work if the work is
prepared by Caster in the scope of Caster's Consultancy, or, if the work is not
prepared by Caster within the scope of Caster's Consultancy but is specially
ordered by Company as a contribution to a collective work, as a part of a motion
picture or other audiovisual work, as a translation, as a supplementary work, as
a compilation, or as an instructional text, then the work shall be considered to
be work made for hire and Company shall be the author of the work.

     4.   During the term of Caster's Consultancy, and for a period of not more
than one hundred eighty (180) days after the termination of Caster's
Consultancy, to the extent necessary to allow the use of existing material
stocks prepared prior to the termination of Caster's Consultancy,  Caster grants
to a Mannatech a non-exclusive, royalty-free, world-wide license to use Caster's
name, voice, likeness, and similar characteristics (the "Licensed Rights") for
the

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purposes of advertising, promoting, selling and otherwise merchandising
Mannatech products and services in connection with Caster's services retained
under this Agreement. Mannatech shall be the sole owner and subject to the terms
of such license will have the use and control of all promotional materials and
trade literature ("Promotional Materials") produced for Mannatech bearing
Caster's image, likeness, voice or name. Mannatech will use the Licensed Rights
only upon or in connection with the usages contemplated by this Section 4 and in
accordance with reasonable standards of quality specified or approved by Caster
from time to time. All Promotional Materials incorporating the Licensed Rights
will be subject to Caster's prior approval, which will not be unreasonably
withheld, for the purpose of assuring the quality and accuracy of the
Promotional Materials. Mannatech shall, subject to the terms of the license
granted hereby, be free to dispose of and treat in any way all Promotional
Materials as contemplated hereby, including but not limited to selling,
advertising, distributing, and using in other mediums.

                                  ARTICLE V.
                                 MISCELLANEOUS

     1.   Termination.

          a.   Commencing on August 1, 2000 (60 days after signing) either of
               Mannatech or Caster may, upon thirty (30) days prior written
               notice (a "Termination Notice") terminate Caster's Consultancy.
               Each of Mannatech and Caster agrees that if they provide a
               Termination Notice, (i) it will include a reasonably complete
               summary statement of the reason for the giving of such notice,
               (ii) each party will undertake reasonable efforts to resolve any
               conflict, disagreement or failure of either party to perform its
               obligations under this Agreement so as to permit the Consultancy
               to continue, and (iii) the CEO, Caster and members of the Board
               of Directors will meet at such reasonable times and places as any
               of them may request in order to attempt to resolve any such
               conflict, disagreement or failure of either party to perform its
               agreements hereunder.  If the parties are unable to resolve such
               matter, then the termination of Caster's Consultancy will become
               effective on the date stated in the Termination Notice.  Delivery
               of a Termination Notice will be Mannatech's exclusive remedy with
               respect to any claim that Caster has breached any of his
               obligations  set forth in Article I, Article II, Sections 1 and 2
               or Article IV.  Upon any termination of Caster's Consultancy
               pursuant to this Section 1.a., or upon termination of Caster's
               Consultancy in conjunction with the termination of this Agreement
               upon any anniversary date pursuant to Article I, Section 1,
               Caster will be paid, as severance (the "Severance Payment"), an
               amount equal to $300,000, plus an additional amount equal to
               $25,000 for each full calendar month of Caster's Consultancy, to
               a maximum of twelve months (or a total of $300,000).  The
               Severance Payment will be paid in

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               twelve equal monthly installments commencing on the date of the
               termination of Caster's Consultancy.

          b.   This Agreement will terminate upon Caster's death.

     2.   Enforcement.  It is the express intention of the parties to this
Agreement to comply with all laws applicable to the covenants and provisions
contained in this Agreement. If any of the covenants contained in this Agreement
are found to exceed in duration or scope those permitted by law, it is expressly
agreed that such covenant may be reformed or modified by the award or decree of
an arbitrator, or, if applicable, a final judgment of a court of competent
jurisdiction or other lawful constituted authority, as the case may be, to
reflect a lawful and enforceable duration or scope, and such covenant
automatically shall be deemed to be amended and modified so as to comply with
the arbitration award, decree, judgment or order of such court or authority, as
the case may be. If any one or more of the provisions contained herein shall for
any reason be held invalid, illegal or unenforceable in any respect even after
reformation, such invalidity, illegality or unenforceability shall not affect
the enforceability or validity of any other provision contained in this
Agreement, and this Agreement shall be construed as if such invalid, illegal, or
unenforceable provisions had never been contained herein.

     3.   Adequacy of Consideration; Separate Agreements.  Caster agrees that
the agreements, non-competition agreements, nondisclosure agreements, and non-
solicitation agreements set forth herein each constitute separate agreements,
independently supported by good and adequate consideration and shall be
severable from the other provisions of this Agreement and shall survive the
Agreement. If a court of competent jurisdiction determines that any restriction
in a clause or provision of this Agreement is void, illegal or unenforceable,
the other clauses and provisions of this Agreement shall remain in full force
and effect and the clauses and provisions that are determined to be void,
illegal or unenforceable shall be limited so that they shall remain in effect to
the fullest extent permitted by law.

     4.   No Indirect Breach.  Caster will use his reasonable efforts to ensure
that no corporation or other entity of which he is an officer, principal,
manager, director or owner of more the 5% of the voting securities or other
affiliate, shall take any action that Caster could not take without violating
any provision of this Agreement.

     5.   Injunctive Relief.  Caster recognizes and acknowledges that damages
in the event of his breach of certain provisions of this Consultancy Agreement
would be inadequate, and Caster agrees that Mannatech, in addition to all other
remedies it may have, shall have the right to injunctive relief or Article III
if there is a breach by Caster of any one or more of the provisions contained in
Article II hereof.

     6.   Arbitration.  Arbitration, including the right to invoke permanent
injunctive relief, shall be the exclusive remedy for any and all disputes,
claims or controversies, whether statutory, contractual or otherwise, between
Mannatech and Caster concerning the Consultancy

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or the termination thereof, provided that either party may apply to a state or
federal court of appropriate jurisdiction in Dallas County, Texas for interim,
temporary, or preliminary relief, including relief by restraining order or
preliminary injunction, in connection with any alleged breach or threatened or
imminent breach of any provision of this Agreement and in aid of the arbitration
provisions herein. By providing for such interim relief or preliminary relief in
the courts of Dallas County, Texas, the parties agree that they are not waiving
the mandatory arbitration provisions herein. In the event either party provides
a Notice of Arbitration of Dispute to the other party, Mannatech and Caster
agree to submit such dispute or controversy, whether statutory or otherwise, to
an arbitrator or arbitrators selected from a panel of arbitrators of the
American Arbitration Association located in Dallas, Texas. The effective rules
at the time of the commencement of the Commercial Arbitration of the American
Arbitration Association shall control the arbitration. In any arbitration
proceeding conducted subject to these provisions, all statutes of limitations
that would otherwise be applicable shall apply to any arbitration proceeding
hereunder. In any arbitration proceeding conducted subject to these provisions,
the arbitrator(s) is/are specifically empowered to decide any question
pertaining to limitations, and may do so by documents or by a hearing, in his or
her sole discretion. In this regard, the arbitrator may authorize the submission
of pre-hearing motions similar to a motion to dismiss or for summary
adjudication for the purposes of consideration of this matter. The arbitrator's
decision will be final and binding upon the parties. The parties further agree
to abide by and perform any award rendered by the arbitrator(s). The prevailing
party in such proceeding shall be entitled to record and have awarded its
reasonable attorney's fees, in addition to any other relief to which it may be
entitled. In rendering the award, the arbitrator(s) shall state the reasons
therefor, including any computations of actual damages or offsets, if
applicable.

     7.   Waiver of Breach.  The waiver by any party hereto of a breach of any
provision of this Agreement shall not operate or be construed as a waiver of any
subsequent breach by any party.

     8.   Entire Agreement.  This Agreement contains the entire agreement of the
parties hereto.  No modification or amendment of this Agreement may be made
except by written agreement signed by both of the parties hereto.

     9.   Descriptive Headings.  All headings, captions and arrangements used in
this Agreement are intended solely for the convenience of the parties and shall
not be deemed to limit, amplify or modify the terms of this Agreement nor affect
the meaning thereof.

     10.  Governing Law.  The substantive laws of the State of Texas, excluding
any conflicts of law rule or principle that might otherwise refer to the
substantive law of another jurisdiction, shall govern the interpretation,
validity and effect of this Agreement without regard to the place for
performance thereof. This Agreement has been executed and delivered by the
parties hereto in Dallas County, Texas, and Mannatech and Caster agree that
exclusive venue as to any action which might ensue before or after arbitration
shall lie, to the extent permitted by the

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Texas and Federal Arbitration Acts within the State or Federal Courts in Dallas
County, Texas to decide any matter relating to this Agreement or the related
arbitration.

     11.  Notices.  Any notice or communication required or permitted hereby
shall be in writing and shall be delivered personally, sent by prepaid telegram
and followed with a confirming letter, or mailed by certified or registered
mail, postage prepaid.

     (a)  If to Caster, to:
          Samuel L. Caster
          2034 W. Beltline Road
          Cedar Hill, Texas 75014

     (b)  If to Mannatech, to:
          Mannatech, Incorporated
          600 S. Royal Lane, Suite 200
          Coppell, Texas 75019

or in the case of each party hereto, to such other address and to the attention
of such other person as may have theretofore been specified in writing in like
manner by such party to the other party.  Each such notice or communication
shall be deemed to have been given as of the date so delivered or at the
expiration of the third business day following the date of the mailing.

     12.  Assignment.  This Agreement shall insure to the benefit of and be
binding upon Mannatech and Caster and their respective successors and assigns.
Neither party shall be entitled to assign any rights or obligations hereunder
without the prior written consent of the other party.

     13.  Prior Agreement.  This Agreement supersedes all prior agreements, if
any, between the parties of any and every nature whatsoever, including
agreements for additional compensation or benefits. All such prior agreements
are null and void, except that Article I of Caster's Employment Agreement dated
May 14, 1997 remains in effect as to confidential information received prior to
his resignation on May 3, 2000.

     14.  Caster Acknowledgement.  Caster affirms and attests by signing this
Agreement that Caster has read this Agreement before signing it and that Caster
fully understands its purposes, terms, and provisions, which Caster hereby
expressly acknowledges to be reasonable in all respects.  Caster further
acknowledges receipt of one (1) copy of this Agreement.

                                       12
<PAGE>

IN WITNESS WHEREOF, this Agreement is executed by the parties hereto, effective
as of the 1st day of June, 2000.

CASTER:                                 MANNATECH:

                                        MANNATECH, INCORPORATED
                                        A Texas Corporation

/s/ Samuel L. Caster                    By:  /s/ Robert M. Henry
--------------------                        --------------------
Samuel L. Caster                                 Robert M. Henry
                                        Its:     Chief Executive Officer

                                       13<PAGE>

                                                                   EXHIBIT 10.26

                            MANNATECH, INCORPORATED
                            2000 STOCK OPTION PLAN

1.  Purpose of the Plan.  The purpose of this 2000 Stock Option Plan is to
    -------------------
    attract and retain the best available personnel for positions of substantial
    responsibility, to provide additional incentive to the Employees of the
    Company and to promote the success of the Company's business and reward
    directors and consultants of the Company.

2.  Definitions.  As used herein, the following definitions shall apply:
    -----------

    (a)   "Code" shall mean the Internal Revenue Code of 1986.
           ----

    (b)   "Common Stock" shall mean the Common Stock of the Company.
           ------------

    (c)   "Company" shall mean Mannatech, Incorporated, a Texas corporation.
           -------

    (d)   "Option Committee" shall mean the Option Committee appointed by the
           ----------------
          Board of Directors in accordance with paragraph (a) of Section 4 of
          the Plan.

    (e)   "Continuous Status as an Employee " shall mean the absence of any
           --------------------------------
          interruption or termination of service as an Employee. Continuous
          Status as an Employee shall not be considered interrupted in the case
          of sick leave, military leave, or any other leave of absence approved
          by the Option Committee; provided that such leave is for a period of
          not more than 90 days or reemployment upon the expiration of such
          leave is guaranteed by contract or statute.

    (f)   "Employee" shall mean any person, including officers and directors,
           --------
          employed by the Company or any Parent or Subsidiary of the Company.
          The payment of a director's fee by the Company shall not be sufficient
          to constitute "employment" by the Company.

    (g)   "Incentive Stock Option" shall mean an Option intended to qualify as
           ----------------------
          an incentive stock option within the meaning of Section 422 of the
          Code.

    (h)   "Non-Employee Director" shall mean a Non-Employee Director as defined
           ---------------------
          in Rule 16b-3 of the Securities Exchange Act of 1934, as amended (the
          "Exchange Act"), promulgated under SEC Release 34-37260 (May 31,
          1996), as such Rule may be amended from time to time.

    (i)   "Option" shall mean a stock option granted pursuant to the Plan.
           ------

    (j)   "Optioned Stock" shall mean the Common Stock subject to an Option.
           --------------

    (k)   "Optionee" shall mean an Employee who receives an Option.
           --------

                                       1
<PAGE>

    (l)   "Parent" shall mean a "parent corporation", whether now or hereafter
           ------
          existing, as defined in Section 425(e) of the Code.

    (m)   "Plan" shall mean this 2000 Stock Option Plan.
           ----

    (n)   "Stock Option Agreement" shall mean a Stock Option Agreement, pursuant
           ----------------------
          to which Options are granted under the Plan.

    (o)   "Share" shall mean a share of the Common Stock, as adjusted in
           -----
          accordance with Section 11 of the Plan.

    (p)   "Subsidiary" shall mean a "subsidiary corporation", whether now or
           ----------
          hereafter existing, as defined in Section 425(f) of the Code.

3.  Stock Subject to the Plan.  Subject to the provisions of Section 11 of the
    -------------------------
    Plan, the maximum aggregate number of shares, which may be optioned and sold
    under the Plan, is 2,000,000 shares of common stock.  The Shares may be
    authorized, but unissued or reacquired common stock.

          If an Option should expire or become unexercisable for any reason
    without having been exercised in full, the unpurchased Shares, which were
    subject thereto, shall, unless the Plan shall have been terminated, become
    available for future grant under the Plan.

4.  Administration of the Plan.
    --------------------------

    (a)   Procedure.  The Plan shall be administered by the Option Committee
          ---------
          consisting of not less than two Non-Employee Directors to administer
          the Plan, subject to such terms and conditions as the Board of
          Directors may prescribe. From time to time the Board of Directors may
          increase the size of the Option Committee and appoint additional
          members thereof, remove members (with or without cause) and appoint
          new members in substitution therefore, fill vacancies however caused,
          or remove all members of the Option Committee and thereafter directly
          administer the Plan.

    (b)   Powers of the Option Committee. Subject to the provisions of the Plan,
          ------------------------------
          the Option Committee shall have the authority, in its discretion to
          grant Non-qualified Stock Options and Incentive Stock Options, in
          accordance with Section 422 of the Code; to determine, upon review of
          relevant information and in accordance with Section 8(b) of the Plan,
          the fair market value of the Common Stock; to determine the exercise
          price per share of Options to be granted, which exercise price shall
          be determined in accordance with Section 8(a) of the Plan; to
          determine the Employees to whom, and the time or times at which,
          Options shall be granted and the number of shares to be represented by
          each Option; to interpret the Plan; to prescribe, amend and rescind
          rules and regulations relating to the Plan; to determine the terms and
          provisions of each Option granted (which need not be

                                       2
<PAGE>

          identical) and, with the consent of the holder thereof, modify or
          amend each Option; to accelerate or defer (with the consent of the
          Optionee) the exercise date of any Option, consistent with the
          provisions of Section 5 of the Plan; to authorize any person to
          execute on behalf of the Company any instrument required to effectuate
          the grant of an Option previously granted by the Option Committee; and
          to make all other determinations deemed necessary or advisable for the
          administration of the Plan.

    (c)   Effect of Option Committee's Decision. All decisions, determinations
          -------------------------------------
          and interpretations of the Option Committee shall be final and binding
          on all Optionees and any other holders of any Options granted under
          the Plan.

5.  Eligibility.
    -----------

    (a)   Incentive Stock Options may be granted only to Employees. An Employee,
          who has been granted an Option may, if such Employee is otherwise
          eligible, is granted an additional Option or Options.

    (b)   The Plan shall not confer upon any Optionee any right with respect to
          continuation of employment with the Company nor shall it interfere in
          any way with Optionee's right or the Company's right to terminate
          Optionee's employment at any time.

6.  Term of Plan.  The Plan shall become effective upon by the adoption by the
    ------------
    Option Committee and the approval by the shareholders of the Company as
    described in Section 17 of the Plan. It shall continue in effect for a term
    of ten (10) years unless sooner terminated under Section 13 of the Plan.

7.  Term of Option.  The term of each Option shall be ten (10) years from the
    --------------
    date of grant thereof or such shorter term as may be provided in the Stock
    Option Agreement. However, in the case of an Option granted to an Optionee
    who, at the time the Option is granted, owns stock representing more than
    ten percent (10%) of the voting power of all classes of stock of the Company
    or any Parent or Subsidiary, the term of the Option shall be five (5) years
    from the date of grant thereof or such shorter time as may be provided in
    the Stock Option Agreement.

8.  Exercise Price and Consideration.
    --------------------------------

    (a)   The per Share exercise price for the Shares to be issued pursuant to
          exercise of an Option shall be such price as is determined by the
          Option Committee, but shall be subject to the following:

          (i)  In the case of an Option granted to an Employee, director or
               consultant, who, at the time of the grant of such Option, owns
               stock representing more than ten percent (10%) of the voting
               power of all classes of stock of the Company or any Parent or
               Subsidiary, the per Share exercise price shall be no less than
               110% of the fair market value per Share on the date of grant.

                                       3
<PAGE>

          (ii) In the case of an Option granted to any other Employee, director
               or consultant, the per Share exercise price shall be no less than
               100% of the fair market value per Share on the date of grant.

    (b)   The fair market value per share shall be determined using the quoted
          closing sale price per share as reported by Nasdaq National Market.

    (c)   The consideration to be paid for the Shares to be issued upon exercise
          of an Option, including the method of payment, shall be determined by
          the Option Committee and may consist entirely of cash, certified or
          official bank check, other Shares of the Company's Common Stock having
          a fair market value on the date of surrender equal to the aggregate
          exercise price of the Shares as to which said Option shall be
          exercised, or any combination of such methods of payment, or such
          other consideration and method of payment for the issuance of Shares
          to the extent permitted under the Texas Business Corporation Act.

9.  Exercise of Option
    ------------------

    (a)   Procedure for Exercise; Rights as a Shareholder.  Any Option granted
          -----------------------------------------------
          hereunder shall be exercisable at such times and under such conditions
          as determined by the Option Committee, including performance criteria
          with respect to the Company and/or the Optionee, and as shall be
          permissible under the terms of the Plan.

          (i)  An Option may not be exercised for a fraction of a Share.

          (ii) An Option shall be deemed to be exercised when written notice of
               such exercise has been given to the Company in accordance with
               the terms of the Option by the person entitled to exercise the
               Option and full payment for the Shares with respect to which the
               Option is exercised has been received by the Company. Full
               payment, as authorized by the Option Committee, may consist of a
               consideration and method of payment allowable under section 8(c)
               of the Plan. Until the issuance (as evidenced by the appropriate
               entry on the books of the Company or of the duly authorized
               transfer agent of the Company) of the stock certificate
               evidencing such Shares, no right to vote or receive dividends or
               any other rights as a shareholder shall exist with respect to the
               Optioned Stock, notwithstanding the exercise of the Option. No
               adjustment will be made for a dividend or other right for which
               the record date is prior to the date the stock certificate is
               issued, except as provided in Section 11 of the Plan. Prior to
               the time of issuance, the Company shall satisfy its employment
               tax and other tax withholding obligations by requiring the
               Optionee to pay the amount of withholding tax, if any, that must
               be paid under federal, state and local law due to the exercise of
               the Option, subject to such restrictions or procedures as the
               Company deems necessary to satisfy Rule 16b-3 of the Exchange
               Act. The payment of such withholding tax may be by certified or
               official bank check or by the delivery of a number of shares of
               Common Stock

                                       4
<PAGE>

               (plus cash if necessary) having a fair market value equal to the
               amount of such withholding tax.

         (iii) Exercise of an Option in any manner shall result in a decrease in
               the number of Shares which thereafter may be available, both for
               purposes of the Plan and for sale under the Option, by the number
               of Shares as to which the Option is exercised.

    (b)   Termination of Status as an Employee. If any Employee ceases to serve
          ------------------------------------
          as an Employee, such Employee may, but only within thirty (30) days
          after the date such person ceases to be an Employee, exercise his or
          her Option to the extent that such person was entitled to exercise it
          at the date of such termination. To the extent that such Employee was
          not entitled to exercise the Option at the date of such termination,
          or if such Employee does not exercise such Option (which such person
          was entitled to exercise) within the time specified herein, the Option
          shall terminate.

    (c)   Disability of Optionee. Notwithstanding the provisions of Section 9(b)
          ----------------------
          above, in the event an Employee is unable to continue his or her
          employment relationship with the Company as a result of such
          Employee's total and permanent disability (as defined in Section
          22(e)(3) of the Code), such Employee may, but only within six (6)
          months (or such other period of time not exceeding twelve (12) months
          as is determined by the Option Committee at the time of grant of the
          Option) from the date of termination, exercise his or her Option to
          the extent such person was entitled to exercise it at the date of such
          termination. To the extent that the Employee was not entitled to
          exercise the Option at the date of termination, or if such Employee
          does not exercise such Option (which such person was entitled to
          exercise) within the time specified herein, the Option shall
          terminate.

    (d)   Death of Optionee.  In the event of the death of an Optionee:
          -----------------

          (i)  During the term of the Option who is at the time of his or her
               death an Employee and who shall have been in Continuous Status as
               an Employee or director or consultant since the date of grant of
               the Option, the Option may be exercised, at any time within six
               (6) months following the date of death, by the Optionee's estate
               or by a person who acquired the right to exercise the Option by
               bequest or inheritance.

10. Non-Transferability of Options.  The Option may not be sold, pledged,
    ------------------------------
    assigned, hypothecated, transferred, or disposed of in any manner other than
    by will or by the laws of descent or distribution and may be exercised,
    during the lifetime of the Optionee, only by the Optionee.

11. Adjustments Upon Changes in Capitalization or Merger.  Subject to any
    ----------------------------------------------------
    required action by the shareholders of the Company, the number of shares of
    Common Stock covered by each outstanding Option, and the number of shares of
    Common Stock which have been authorized for issuance under the Plan but as
    to which no Options

                                       5
<PAGE>

    have yet been granted or which have been returned to the Plan upon
    cancellation or expiration of any Option, as well as the price per share of
    Common Stock covered by each such outstanding Option, shall be
    proportionately adjusted for any increase or decrease in the number of
    issued shares of Common Stock resulting from a stock split, reverse stock
    split, stock dividend, combination or reclassification of the Common Stock,
    or any other increase or decrease in the number of issued shares of Common
    Stock effected without receipt of consideration by the Company; provided,
    however, that conversion of any convertible securities of the Company shall
    not be deemed to have been "effected without receipt of consideration." Such
    adjustment shall be made by the Option committee, whose determination in
    that respect shall be final, binding and conclusive. Except as expressly
    provided herein, no issuance by the Company of shares of stock of any class,
    or securities convertible into shares of stock of any class, shall affect,
    and no adjustment by reason thereof shall be made with respect to, the
    number or price of shares of Common Stock subject to an Option.

          In the event of the proposed dissolution or liquidation of the
    Company, the Option will terminate immediately prior to the consummation of
    such proposed action, unless otherwise provided by the Option Committee. The
    Option Committee may, in the exercise of its sole discretion in such
    instances, declare that any Option shall terminate as of a date fixed by the
    Option Committee and give each Optionee the right to exercise his or her
    Option as to all or any part of the Optioned Stock, including Shares as to
    which the Option would not otherwise be exercisable. In the event of the
    proposed sale of all or substantially all of the assets of the Company, or
    the merger of the Company with or into another corporation, the Option shall
    be assumed or an equivalent option shall be substituted by such successor
    corporation or a parent or subsidiary of such successor corporation, unless
    the Option Committee determines, in the exercise of its sole discretion and
    in lieu of such assumption or substitution, that the Optionee shall have the
    right to exercise the Option as to all of the Optioned Stock, including
    Shares as to which the Option would not otherwise be exercisable. If the
    Option Committee makes an Option fully exercisable in lieu of assumption or
    substitution in the event of a merger or sale of assets, the Option
    Committee shall notify the Optionee that the Option shall be fully
    exercisable for a period of thirty (30) days from the date of such notice,
    and the Option will terminate upon the expiration of such period.

12. Time of Granting Options.  The date of grant of an Option shall be the date
    ------------------------
    on which the Option Committee makes the determination granting such Option.
    Notice of the determination shall be given to each Optionee to whom an
    Option is so granted within a reasonable time after the date of such grant.

                                       6
<PAGE>

13. Amendment and Termination of the Plan.
    -------------------------------------

    (a)   Amendment and Termination. The Option Committee may amend or terminate
          -------------------------
          the Plan from time to time in such respects as the Option Committee
          may deem advisable; provided that, the following revisions or
          amendments shall require approval of the shareholders of the Company
          in the manner described in Section 17 of the Plan:

          (i)  An increase in the number of Shares subject to the Plan above
               2,000,000 Shares, other than in connection with an adjustment
               under Section 11 of the Plan;

    (b)   Effect of Amendment or Termination. Any such amendment or termination
          ----------------------------------
          of the Plan shall not affect Options already granted and such Options
          shall remain in full force and effect as if the Plan had not been
          amended or terminated, unless mutually agreed otherwise between the
          Optionee and the Option Committee, which agreement must be in writing
          and signed by the Optionee and the Company.

14. Conditions Upon Issuance of Shares.  Shares shall not be issued pursuant to
    ----------------------------------
    the exercise of an Option unless the exercise of such Option and the
    issuance and delivery of such Shares pursuant thereto shall comply with all
    relevant provisions of law, including, without limitation, the Securities
    Act of 1933, as amended, the Exchange Act, the rules and regulations
    promulgated thereunder, applicable state securities laws, and the
    requirements of the Nasdaq National Market upon which the Shares are listed,
    and shall be further subject to the approval of general in-house counsel for
    the Company with respect to such compliance.

    (a)   As a condition to the exercise of an Option, the Company may require
          the person exercising such Option to represent and warrant at the time
          of any such exercise that the Shares are being purchased only for
          investment and without any present intention to sell or distribute
          such Shares if, in the opinion of general in-house counsel for the
          Company, such a representation is required by any of the
          aforementioned relevant provisions of law.

15. Reservation of Shares.  The Company, during the term of this Plan, will at
    ---------------------
    all times reserve and keep available 2,000,000 Shares as shall be sufficient
    to satisfy the requirements of the Plan.

    (a)   Inability of the Company to obtain authority from any regulatory body
          having jurisdiction, which authority is deemed by the Company's
          general in-house counsel to be necessary to the lawful issuance and
          sale of any Shares hereunder, shall relieve the Company of any
          liability in respect of the failure to issue or sell such Shares as to
          which such requisite authority shall not have been obtained.

16. Option Agreement.  Options shall be evidenced by written option agreements
    ----------------
    in such form, as the Option Committee shall approve.

                                       7
<PAGE>

17. Shareholder Approval.  Continuance of the Plan shall be subject to approval
    --------------------
    by the shareholders of the Company within twelve months before or after the
    date, the Plan is adopted. If such shareholder approval is obtained at a
    duly held shareholders meeting, it may be obtained by the affirmative vote
    of the holders of a majority of the outstanding shares of the Company, such
    holders being present or represented and entitled to vote thereon.

18. Information to Optionees.  The Company shall provide to each Optionee,
    ------------------------
    during the period for which such Optionee has one or more Options
    outstanding, copies of all annual reports and other information which are
    provided to all shareholders of the Company. The Company shall not be
    required to provide such information if the issuance of Options under the
    Plan is limited to key employees whose duties in connection with the Company
    assure their access to equivalent information.

19. CHOICE OF LAW.  THE CORPORATE LAW OF THE STATE OF TEXAS WILL GOVERN ALL
    -------------
    QUESTIONS CONCERNING THE RELATIVE RIGHTS OF THE COMPANY AND ITS
    SHAREHOLDERS. ALL OTHER QUESTIONS CONCERNING THE CONSTRUCTION, VALIDITY AND
    INTERPRETATION OF THIS PLAN AND THE INSTRUMENTS EVIDENCING OPTIONS WILL BE
    GOVERNED BY THE INTERNAL LAW, AND NOT THE LAW OF CONFLICTS, OF THE STATE OF
    TEXAS.

    IN WITNESS WHEREOF, the Company has caused its duly authorized officer to
execute this Plan effective as of the 28th day of April, 2000.

                                   MANNATECH, INCORPORATED

                                   By:   /s/ Robert M. Henry
                                      ----------------------
                                   Name: Robert M. Henry
                                        ----------------
                                   Title: Chief Executive Officer
                                         ------------------------

                                       8

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