<PAGE>   1
                                                                   EXHIBIT 10.15


                                    AGREEMENT


This Agreement is made as of the 26th day of January, 1996 between Genelabs
technologies, Inc., a California corporation with its principal place of
business at 505 Penobscot Drive, Redwood City, California 94063 ("Genelabs") and
Dr. Edgar G. Engleman, an individual, whose residence is 60 Lane Place,
Atherton, California 94025 ("Engleman").


                                    RECITALS


         A.  Engleman is a member of the Board of Directors of Genelabs,
             Chairman of the Scientific Advisory Board of Genelabs and a
             consultant to Genelabs.

         B.  In his capacity as a consultant to Genelabs, Engleman has
             identified as a potential commercial opportunity for Genelabs the
             use of a compound known as dehydroepiandrosterone ("DHEA") in the
             treatment of systemic lupus erythematosus ("SLE"), a disease that
             can inflame and damage the connective tissue in various parts of
             the human body.

         C.  Engleman has assisted Genelabs in obtaining from Stanford
             University a license to certain rights and clinical data relating
             to the use of DHEA in the treatment of SLE.

         D.  Genelabs is in the process of clinical testing and development for
             DHEA for the treatment of SLE, and intends to commercialize a
             therapeutic product using DHEA for the treatment of SLE.

         E.  With the approval of a majority of its Board of Directors other
             than Engleman (who abstained with respect of this matter), Genelabs
             has agreed to compensate Engleman for his identification of the
             application of DHEA to SLE and for his assistance in obtaining the
             rights referred to above, as set forth in this Agreement.

NOW, THEREFORE, Genelabs and Engleman agree as follows:

         1.  Fees. In the event that Genelabs or any licensee of Genelabs sells
             any product that incorporates DHEA for the treatment of SLE (a
             "Product"), Genelabs will pay fees to Engleman, subject to the
             terms of this Agreement, as follows:

                  (a) a fee equal to [ * ] of the Net Sales of Products by
                      Genelabs or any affiliate of Genelabs during the term of
                      this Agreement; and

                  (b) a fee equal to the lesser of (i) [ * ] of the Net Sales of
                      Products by any licensee that is not an affiliate of
                      Genelabs or (ii) [ * ] of the amounts actually received by
                      Genelabs with respect to the Net Sales of Products by such
                      licensee, during the term of this Agreement.

[*]      Confidential treatment requested pursuant to a request for confidential
         treatment filed with the Securities and Exchange Commission. Omitted
         portions have been filed separately with the Commission.

                                       1
<PAGE>   2

The term of this Agreement shall expire upon the seventeenth (17th) annual
anniversary of the first commercial sale of a Product made by Genelabs or a
licensee, after which Genelabs will have no further obligations to Engleman
under this Agreement except for payment of any amounts then due hereunder.

For purposes of this Section, an "affiliate" means any corporation or other
business entity that is controlled by Genelabs, where "control" means ownership
of a majority of the equity interests or the power to elect a majority of the
directors or other members of the governing body of the entity.

         2.  Determination of Net Sales.

                  (a) Net Sales. As used in this agreement, "Net Sales" or any
                      Product will mean the aggregate worldwide gross revenues
                      that are recognized and actually received by Genelabs, its
                      affiliates or its licensees from or on account of the sale
                      of Products to independent third parties, less (i)
                      reasonable credits or allowances, if any, actually granted
                      on account of, and reasonably allocable to, Products,
                      based on price adjustments, discounts or rebates to such
                      independent third parties, (ii) reasonable credits or
                      allowances, if any, actually granted on account of
                      recalls, rejection or return of Products previously sold,
                      (iii) excises, sales taxes, consumption taxes, duties or
                      other taxes imposed upon and paid with respect to such
                      sales (excluding income or franchise taxes of any kind)
                      and (iv) separately itemized transportation and insurance
                      costs incurred in shipping Products to such independent
                      third parties.

                  (b) Exclusions. Net Sales will not include any revenues
                      received by any licensee of Genelabs with respect to
                      Products manufactured by such licensee and transferred to
                      Genelabs for resale of Genelabs but will include revenues
                      from resale by Genelabs. No transfer of Products solely
                      for experimental purposes or as samples will be considered
                      a sale for purposes of determining Net Sales.

                  (c) Products Sold in Combination. If Genelabs or any of its
                      affiliates or licensees sells Products together with other
                      products to independent third parties at a combined price,
                      then the Net Sales for the Product will be to the average
                      price for "arms length" sales of Products sold separately
                      during the fee reporting period in which such sales occur.

         3.  Reports and Payments. Genelabs will deliver to Engleman within 45
             days after the end of each calendar quarter a written report
             showing its computation of fees due under this Agreement and with
             respect to (a) Net Sales made by Genelabs or its affiliates during
             such calendar quarter and (b) payments received by Genelabs or its
             affiliates from licensees that are not affiliates of Genelabs
             during such quarter with respect to Net Sales by such licensees.

         4.  Inspection of Records. Genelabs will keep, and will require its
             affiliates and licensees to keep, complete and accurate books and
             records necessary to verify the Net Sales of Products and the
             payment of fees hereunder. During the term that fees are payable
             under this Agreement and for one year after the date of the last
             fee payment, Engleman will have the right at his expense to have an
             independent auditor inspect such books


                                       2
<PAGE>   3

             and records at reasonable times and upon reasonable notice, but not
             more often than once each calendar year. If such inspection reveals
             an underpayment by Genelabs of more than 5% of the fees determined
             by such inspection to be due for the period inspected, Genelabs
             will pay the reasonable fees and expenses for such auditor for such
             inspection. Neither Engleman nor the auditor will disclose the Net
             Sales of Products to any third party except as may be necessary to
             enforce Engleman's rights to receive fees under this Agreement.

         5.  General.

                  (a) Governing Law. This Agreement will be governed by and
                      enforced in accordance with the laws of the State of
                      California.

                  (b) Notices. Any notice or report required or permitted to be
                      given hereunder shall be given in writing and deemed
                      sufficient if sent by first class mail or hand delivered
                      to the respective party at the address set forth on the
                      first page of this Agreement, or any subsequent address
                      provided by notice hereunder. Any such notice or report
                      given by mail shall be deemed to have been given when
                      mailed.

                  (c) Assignment. This Agreement shall be assignable by Genelabs
                      to any third party to which Genelabs assigns substantially
                      all of its rights to make, use and sell Products in the
                      treatment of SLE, provided that the third party expressly
                      assumes all of Genelabs' obligations hereunder and
                      Genelabs remains responsible for all obligations of the
                      third party hereunder. Genelabs may license any affiliate
                      or third party to make, use or sell Products, subject to
                      the payment of fees under this Agreement. The rights to
                      receive payment hereunder may be assignable by Engleman to
                      the Engleman Family Trust.

                  (d) Arbitration. Any dispute, controversy or claim arising out
                      of or relating to this Agreement, or the breach thereof,
                      shall be settled by arbitration in San Mateo County,
                      California, in accordance with the rules of the American
                      Arbitration Association then in effect, and the prevailing
                      party shall be awarded such party's costs and expenses,
                      including reasonable attorneys' fees. Judgment upon the
                      award of the arbitrator(s) may be entered in any court
                      having jurisdiction thereof.

                  (e) Entire Agreement. This Agreement constitutes the entire
                      understanding between the parties with respect to the
                      subject matter hereof and supersedes all previous
                      negotiations, representations and understandings between
                      the parties with respect thereto. No waiver or amendment
                      of any of the provisions hereof shall be effective unless
                      made in writing and signed by both parties.

                  (f) Waiver. The waiver by either party of a breach of any
                      provision of this Agreement by the other party will not be
                      construed as a waiver of any succeeding breach of the same
                      or any other provision.


                                       3
<PAGE>   4

                  (g) Severability. Should any part of this Agreement be held
                      unenforceable, the unenforceable part of this Agreement
                      shall be replaced with a provision that accomplishes, to
                      the extent possible, the original purpose of the
                      unenforceable provision, and the remainder of the
                      Agreement will remain in effect.


GENELABS:                                    ENGLEMAN:

GENELABS TECHNOLOGIES, INC.

By:  /s/ Irene Chow                          By:  /s/ Edgar G. Engleman
     --------------                               ---------------------
     Irene Chow, Ph.D.                            Edgar G. Engleman, M.D.
     President & CEO


                                       4