EXHIBIT 4.15

                                YORK MEDICAL INC.

                      Joint Venture Shareholders' Agreement

                                November 11, 1995

            Between:   York   Medical   Inc.   ("YM"),   a   company
            incorporated  under the laws of the Province of Ontario,
            Canada,  CBQYM INC.,  a company  incorporated  under the
            laws of the Province of Ontario,  Canada ("CBQYM"),  and
            CIMAB S.A., ("CIMAB") a Cuban company incorporated under
            the laws of the Republic of Cuba, representing Centro de
            Bioactivos  Quimicos of the  Universidad  Central de Las
            Villas ("CBQ").

                                    RECITALS

Whereas:

      |X|   CIMAB entered into a licensing  agreement  with YM on behalf of CBQ,
            dated May 3, 1995 (the "Licensing Agreement");

      |X|   CBQYM has been  incorporated  to serve as a joint  venture  company,
            owned as to 80% of its  common  equity by YM and as to 20% by CIMAB,
            to market the licenced products assigned to it by YM pursuant to the
            Licencing Agreement;

      |X|   Certain of the benefits  and  obligations  of the Licence  Agreement
            have been assigned to CBQYM by YM; and

      |X|   The purpose of this agreement is to set out the relationship between
            the  parties  hereto  so  that  they  will  proceed  on  a  mutually
            beneficial basis.

Now therefore, for good and valuable consideration and the sum of one dollar
(Canadian funds) paid by each party to the other, receipt of which is hereby
acknowledged,


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      |X|   CBQYM shall have an unlimited  number of common shares,  the initial
            issue of which shall be as to 80% to YM and as to 20% to CIMAB.

      |X|   No issued and  outstanding  shares in the  capital of CBQYM shall be
            sold, transferred or otherwise disposed of to any person without the
            written consent of each of YM and CIMAB.

      |X|   The issue of any  additional  common  shares in the capital of CBQYM
            shall  first  be to each of YM and  CIMAB  in  proportion  to  their
            shareholdings,  and thereafter to any other person but only with the
            consent of both of YM and CIMAB,  such  consent  not to be  withheld
            unreasonably.

      |X|   The board of  directors  of CBQYM shall  consist of five  directors,
            three of whom shall be nominees of YM, two of whom shall be nominees
            of CIMAB.  The  initial  directors  of CBQYM  shall be as set out in
            Appendix  A hereto.  The  election  of  directors  shall  take place
            annually ?? board is required to meet once per year,  and  otherwise
            as often as deemed  necessary for the conduct of the business of the
            joint venture in accordance with the Articles of  Incorporation  and
            the  by-laws of CBQYM.  The by-laws of CBQYM  shall  provide  that a
            quorum for meetings of the board of  directors  shall be one of each
            of the YM and CIMAB  nominees,  notice shall be a minimum of 30 days
            prior to any meeting and  meetings  may be called at any time by two
            directors.

      |X|   CBQYM shall use its best efforts to undertake  and perform the terms
            of the assigned Licence Agreement. In all events CBQYM shall operate
            solely through YM in CBQYM's  commercialization of products pursuant
            to the Licence  Agreement,  any assignment thereof and regarding any
            future licencing agreements.

      |X|   All material and out-of-the-ordinary-course of business contracts of
            CBQYM, including contracts or agreements respecting the borrowing of


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            money,   the  issuance  of   guarantees,   the   entering   into  of
            non-arms-length  agreements,  the  lending  of money to any  persons
            related to CBQYM,  the  payment of  dividends  and the  pledging  of
            property  are required to be approved by four fifths of the board of
            directors.  Such approval may be evidenced either by a resolution of
            the board of directors of CBQYM or a written  consent  signed by the
            required number of directors.  Any and all other matters relating to
            the  business and affairs of CBQYM shall be governed by the Articles
            of Incorporation and by-laws or, to the extent not provided in them,
            by a majority of the directors of CBQYM evidenced as provided above.

      |X|   The auditors of CBQYM shall be KPMG Peat  Marwick.  CBQYM's full and
            accurate  records of the Net Revenues  shall be made  available  for
            inspection by CIMAB.

In witness whereof the parties hereto have executed this Agreement by duly
authorized officers or representatives thereof.

CIMAB S.A.                                             YORK MEDICAL INC.


________________________                               _________________________
duly authorized to sign                                duly authorized to sign


CBQYM INC.

________________________
duly authorized to sign


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                                   APPENDIX A

                         INITIAL DIRECTORS OF CBQYM INC.

                           Dr. Ervello Olazabal Manso

                           Ing. Humberto Martin Perez

                              Ezra Solomon Lwowski

                                Hugh B. Anderson

                          Diane Joan Kalina (President)