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                                                                  Exhibit 10.15


                                FIRST AMENDMENT
                                       TO
                    CONVERTIBLE DEBENTURE PURCHASE AGREEMENT


         THIS FIRST AMENDMENT TO CONVERTIBLE DEBENTURE PURCHASE AGREEMENT (the
"Amendment") is entered into as of December 31, 1996, by and between DISC,
Inc., a California corporation (the "Company"), and MK GVD FUND (the
"Purchaser").

                               R E C I T A L S :

         A.      Whereas on March 29, 1996 the Company and Purchaser entered
into a Convertible Debenture Purchase Agreement pursuant to which the Company
agreed to sell, and Purchaser agreed to purchase, an aggregate of $1,400,000 in
principal amount of Convertible Debentures, each convertible into shares of the
Company's Preferred Stock.

         B.      The Company and Optionee now seek to amend the Agreement to
increase the total amount of Convertible Debentures which Purchaser agrees to
purchase thereunder.

         NOW, THEREFORE, for good and valuable consideration, receipt of which
is hereby acknowledged, and in consideration of the mutual covenants set forth
herein, the parties hereto agree as follows:

         1.      DEFINITIONS.  Unless otherwise defined herein, capitalized
terms used in this Amendment shall have the same meanings ascribed to them in
the Convertible Debenture Purchase Agreement.

         2.      AMENDMENTS TO CONVERTIBLE DEBENTURE PURCHASE AGREEMENT.

         (a) Section 1.1(a) of the Convertible Debenture Purchase Agreement is
hereby amended to provide that Purchase agrees to purchase, and the Company
agrees to issue and sell, an aggregate of $3,400,000 in principal amount of
Convertible Debentures.

         (b) Section 2(b) of Exhibit B to the Convertible Debenture Purchase
Agreement is hereby amended to provide that the "Conversion Price" shall be
eighty-five percent (85%) of the closing bid price per share of the Company's
Common Stock as quoted on the Nasdaq Small Cap Market on the last day on or
prior to the Maturity Date.

         3.      ENTIRE AGREEMENT; AMENDMENT.  The Convertible Debenture
Purchase Agreement, as  amended by this Amendment, constitutes the full and
complete agreement and understanding between the parties hereto regarding the
subject matter of the Convertible Debenture Purchase Agreement and shall
supersede all prior communications, representations, understandings or
agreements, if any, whether oral or written, concerning the subject matter
contained in the Convertible Debenture Purchase Agreement, as so amended, and
that no provision of the Convertible Debenture Purchase Agreement, as so
amended, may be modified, amended, waived or discharged, in whole or in part,
except in accordance with its terms.

         4.      FORCE AND EFFECT.  Except as modified by this Amendment, the
terms and provisions of the Convertible Debenture Purchase Agreement are hereby
ratified and confirmed and are and shall remain in full force and effect.
Should any inconsistency arise between this Amendment and the Convertible
Debenture Purchase Agreement as to the specific matters which are the subject
of this Amendment, the terms and conditions of this Amendment shall control.
This Amendment shall
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be construed to be part of the Convertible Debenture Purchase Agreement and
shall be deemed incorporated into the Convertible Debenture Purchase Agreement
by this reference.

         5.      COUNTERPARTS.  This Amendment may be executed in one or more
counterparts, each of which shall be an original but all of which together
shall constitute one instrument.


         IN WITNESS WHEREOF, the Company has caused this Agreement to be
executed in duplicate on its behalf by its duly authorized officer and Optionee
has also executed this Agreement in duplicate, all as of the day and year
indicated above.

                                        DISC, INC.
                                        a California corporation


                                        By: /s/ J. Richard Ellis 
                                            -----------------------------------
                                            J. Richard Ellis, President and
                                            Chief Executive Officer


                                        PURCHASER:

                                        MK GVD FUND


                                        By: /s/ Michael D. Kaufman 
                                            -----------------------------------
                                            Michael D. Kaufman, General Partner