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                                                                   EXHIBIT 10.74



                                  AMENDMENT #3
                           TO COLLABORATION AGREEMENT

This Amendment #3 to Collaboration Agreement (this "Amendment") is made and
entered into as of December 15, 1997, by and between DepoTech Corporation, a
California corporation ("DepoTech") and Chiron Corporation, a Delaware
corporation ("Chiron").

The Collaboration Agreement dated as of March 31, 1994, between Chiron and
DepoTech (the "Collaboration Agreement") was previously amended by Amendment #1
to Collaboration Agreement, dated as of April 1, 1997 ("Amendment #1") and
Amendment #2 to Collaboration Agreement, dated as of June 4, 1997 ("Amendment
#2). 

The parties hereby agree to amend Section 3.B.(i) of Amendment #2 to read in
full as follows:

     The entire $11,700,000 shall be payable upon the date of the earlier of the
          following events (such earlier date referred to as the "Payment
          Date"). If neither event occurs, payment shall be governed by
          subsection (ii) or (iii) below. 

               If, prior to December 31, 1998, the FDA issues a letter of other
                    notification (each an "FDA Notification") indicating that
                    the NDA with respect to DTC 101 in the United States is
                    approvable or approved, the Payment Date shall be the date
                    of the first FDA Notification.

               Notwithstanding subsection (aa) above, if, prior to December 28,
                    1997, at least two-thirds of the voting members of the
                    Oncologic Drugs Advisory Committee to the FDA ("ODAC") (i.e.
                    absent or abstaining members are excluded) vote to recommend
                    that the FDA approve such NDA for the indications submitted,
                    and, at the meeting at which such vote occurs, the ODAC does
                    not recommend any material adverse changes to the product
                    labeling from that submitted in connection with the NDA, the
                    Payment Date shall be the date of such ODAC meeting.

          DepoTech shall, at its option, pay the entire amount in cash within
          five(5) working days after the Payment Date, or deliver to Chiron
          within five(5) working days after the Payment Date a promissory note
          in the form attached hereto as Exhibit A, for the principal amount of
          the unpaid balance. Such note shall be payable in full not later than
          December 31, 1998, and shall bear interest from the Payment Date until
          paid in full at a rate equal to the 12 month Treasury Bill rate on the
          Payment Date plus 150 basis points, not to exceed the maximum rate
          permitted by applicable law.

Except as set forth herein, the Collaboration Agreement, as previously amended
by Amendment #1 and Amendment #2, remains in full force and effect.

Executed by the parties as of the date first written above.

DEPOTECH CORPORATION                            CHIRON CORPORATION

By /s/ EDWARD L. ERICKSON                       By /s/ MAGNUS LUNDBERG
  ------------------------------                  -----------------------------
  (Edward L. Erickson), President                 (Magnus Lundberg), President
  and Chief Executive Officer                     Chiron Therapeutics