EXHIBIT 10.5

                            STOCK PURCHASE AGREEMENT

      This Stock Purchase Agreement (the "Agreement"), dated as of September 28,
2001, is made by and between Mannatech, Incorporated, a Texas corporation (the
"Company") and Ray Robbins, an individual residing in Grand Prairie, Texas
("Purchaser").

      WHEREAS, the Company desires to sell Eight Hundred Fifteen Thousand
(815,000) shares of common stock, $0.0001 par value per share (the "Shares") to
Purchaser, and Purchaser desires to purchase the Shares from Company, subject to
the terms and conditions of this Agreement.

      NOW, THEREFORE, in consideration of the agreements and obligations set
forth herein and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties hereto, intending to
be legally bound, hereby agree as follows:

                             STATEMENT OF AGREEMENT

      1. Purchase and Sale of the Shares. At the Closing (as hereinafter
defined) and upon the terms and subject to the conditions of this Agreement,
Company shall sell, transfer and deliver to Purchaser, and Purchaser shall
purchase from Company, the Shares. At the Closing, Company shall deliver to
Purchaser a certificate or certificates representing the Shares.

      2. Consideration and Payment for the Shares. As consideration for the
purchase of the Shares, Purchaser shall pay to Company the sum of Eight Hundred
Fifteen Thousand Dollars ($815,000.00) (the "Purchase Price"). The Purchase
Price shall be paid at the Closing by wire transfer of immediately available
funds.

      3. Closing. Subject to the conditions contained in this Agreement, the
deliveries contemplated by Sections 1 and 2 hereof (the "Closing") shall take
place at the offices of the Company simultaneously with the execution of this
Agreement.

      4. Representations and Warranties of Purchaser. Purchaser hereby
represents and warrants to Company as follows:

            (a) Authority. Purchaser has full legal capacity to enter into this
Agreement and to consummate the transactions contemplated hereby. This Agreement
has been duly executed and delivered by Purchaser and constitutes a valid and
binding obligation of Purchaser, enforceable in accordance with its terms,
except as enforceability may be limited by bankruptcy, insolvency or other
similar laws or equitable principles affecting the enforcement of creditors'
rights generally.

            (b) Conflict. The execution, delivery and performance of this
Agreement by Purchaser will not conflict with, result in any breach of or
constitute a default under any


agreement, instrument, order, judgment, decree, law or governmental regulation
to which Purchaser is subject.

            (c) Investment Representations.

                  (i) Purchaser understands that the Shares have not been
registered under the Securities Act. Purchaser is acquiring the Shares for
investment purposes only and is not purchasing the Shares with a view to the
sale or distribution of any part thereof.

                  (ii) Purchaser has made such investigation into the Company
that Purchaser considers necessary and appropriate to its purchase of the
Shares, is capable of evaluating the merits and risks of its purchase of the
Shares, and is relying solely upon such investigation and not upon any
representation or warranty made by the Company, other than the representations
and warranties specifically made in this Agreement.

                  (iii) Purchaser qualifies as an "accredited investor" as such
term is defined in Regulation D promulgated under the Securities Act of 1933, as
amended.

      5. Miscellaneous.

            (a) Survival of Representations and Warranties. All representations,
warranties contained herein shall survive the execution and delivery of this
Agreement and the Closing, regardless of any investigation at any time made by
or on behalf of any party hereto.

            (b) Further Assurances. At the Closing and thereafter, from time to
time and without additional consideration, Company and Purchaser, as the case
may be, shall execute and deliver, or cause to be executed and delivered, such
additional or further transfers, assignments, endorsements, consents and other
instruments as Purchaser or Company, as the case may be, may reasonably request
for the purpose of effectively carrying out the transactions contemplated by
this Agreement.

            (c) Successors and Assigns. This Agreement will be binding upon,
inure to the benefit of, and be enforceable by the parties hereto and their
respective successors and assigns.

            (d) Amendments. This Agreement may not be amended, supplemented or
modified except by an instrument in writing signed by each of the parties
hereto.

            (e) Interpretation. The headings contained in this Agreement are for
reference purposes only and shall not affect in any way the meaning or
interpretation of this Agreement.

            (f) Counterparts. This Agreement may be executed in multiple
counterparts, each of which shall be deemed to be an original and which taken
together shall constitute one and the same agreement.


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            (g) Entire Agreement. This Agreement (including the documents and
instruments referred to herein) (i) constitutes the entire agreement and
supersedes all prior agreements and understandings, both written and oral, among
the parties with respect to the subject matter hereof and (ii) is not intended
to confer upon any person other than the parties hereto any rights or remedies
hereunder.

            (h) GOVERNING LAW. THIS AGREEMENT SHALL BE GOVERNED BY AND CONSTRUED
IN ACCORDANCE WITH THE LAWS OF THE STATE OF TEXAS WITHOUT GIVING EFFECT TO THE
CONFLICTS OF LAWS RULES THEREOF. EACH PARTY HERETO AGREES THAT IT SHALL BRING
ANY ACTION OR PROCEEDING IN RESPECT OF ANY CLAIM ARISING OUT OF OR RELATED TO
THIS AGREEMENT OR THE TRANSACTIONS CONTAINED IN OR CONTEMPLATED HEREBY, WHETHER
IN TORT OR CONTRACT OR AT LAW OR IN EQUITY, EXCLUSIVELY IN THE STATE COURTS OF
TEXAS OR THE FEDERAL COURTS OF THE NORTHERN DISTRICT OF TEXAS (THE "CHOSEN
COURTS") AND (i) IRREVOCABLY SUBMITS TO THE EXCLUSIVE JURISDICTION OF THE CHOSEN
COURTS, (ii) WAIVES ANY OBJECTION TO LAYING VENUE IN ANY SUCH ACTION OR
PROCEEDING IN THE CHOSEN COURTS AND (iii) WAIVES ANY OBJECTION THAT THE CHOSEN
COURTS ARE AN INCONVENIENT FORUM OR DO NOT HAVE JURISDICTION OVER ANY PARTY
HERETO.

      IN WITNESS WHEREOF, the parties have executed this Agreement on the date
first above written.

                                        Mannatech, Incorporated

                                        By:  Stephen D. Fenstermacher
                                             -----------------------------------
                                        Its: Chief Financial Officer
                                             -----------------------------------


                                        PURCHASER:

                                        Marlin Ray Robbins
                                        ----------------------------------------
                                        Ray Robbins


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