EXHIBIT 4.17

                                      YORK

                                  MEDICAL INC.

YORK MEDICAL INC.
5045 Orbitor Drive                                             November 23, 1995
Bldg. 11, Suite 400     CBQYM INC.
L4W 4Y4                 5045 Orbitor Drive
                        Building 11, Suite 400

Tel:  (905) 629-9761  Mississauga, Ontario L4W 4Y4
Fax:  (905) 629-4959
Internet:  yorkmed@astral.magic.ca  Dear Sirs:

                              We  refer  to  the   assignment   and   assumption
                        agreement dated as of November 22, 1995 among CBQYM INC.
                        and York  Medical  Inc.  ("YMI")  pursuant  to which YMI
                        assigned  to CBQYM INC.  all of YMI's  right,  title and
                        interest in and to the  Licensing  Agreement (as defined
                        therein).

                              YMI agrees to conduct or arrange  for the  conduct
                        of the  appropriate  studies and clinical  trials of the
                        products and  processes to which CBQYM INC. was assigned
                        rights under the Licence Agreement, and to pay, or cause
                        to be paid,  the cost of any such  studies  and trial so
                        conducted,  subject to  reimbursement  by CBQYM INC.  as
                        described  below.  YMI shall,  in  agreement  with CBQYM
                        INC.,  determine the nature and protocol of any study or
                        trial so conducted.  Notwithstanding the foregoing,  YMI
                        shall have no  obligation  to conduct or arrange for the
                        conduct of any study or trial  where such study or trial
                        would be commercially or scientifically  unreasonable in
                        the  circumstances,  as  determined  by YMI in its  sole
                        discretion.  In  addition,  YMI  shall  pay the  initial
                        organizational  expenses and the administrative expenses
                        of CBQYM INC. which expenses shall  constitute  expenses
                        to be included in the  calculation of the "Net Revenues"
                        described in the Licence  Agreement  between  CBQYM INC.
                        and YMI.

                                                Yours very truly,
                                                York Medical Inc

                                                by:
                                                    ------------------------
                                                    David G.P. Allan
                                                    Chairman


<PAGE>

Accepted and agreed to as of November 23, 1994.

                                CBQYM INC.



                                by:
                                   --------------------------------------



                                by:
                                   --------------------------------------
                                   on behalf of YMI's Nominee
                                   duly authorized to sign

                                by:
                                   --------------------------------------
                                   on behalf of CIMAB S.A's Nominee
                                   duly authorized to sign