EXHIBIT 10.1


                            AMENDMENT NO.1 MARKETING
                           AND CO-PROMOTION AGREEMENT


  This AMENDMENT NO.1 MARKETING AND CO-PROMOTION AGREEMENT (the "Amendment") is
made this _____day of March, 2000, and effective as of January 1, 2000, by and
between C. R. BARD, INC. ("BARD"), a New Jersey corporation with offices at 730
Central Avenue, Murray Hill, New Jersey 07974, and CYTOGEN CORPORATION
("CYTOGEN"), a Delaware corporation with offices at 600 College Road East,
Princeton, New Jersey 08540.

WHEREAS, CYTOGEN and BARD are parties to that certain Marketing and Co-Promotion
Agreement,  dated August 1, 1996 (the  "Agreement"),  pursuant to which  CYTOGEN
granted BARD  certain  rights to market  Products (as defined in the  Agreement)
pursuant to the terms and conditions of the Agreement; and

WHEREAS,  by mutual agreement,  the parties now desire to amend the term and the
compensation  provisions  of the Agreement to enable to the parties to terminate
the Agreement as of the end of June, 2000.

WHEREAS,  the parties now desire to amend the  Agreement as expressly  set forth
below.

NOW,  THEREFORE,  in  consideration of the premises and the mutual covenants and
benefits herein set forth, the parties agree as follows:

1. The parties agree to amend the Agreement as follows:

(A) Section 1.32 of the Agreement,  entitled "Term," is deleted in its entirety,
substituting in lieu thereof the following:

          1.32  Term - shall  mean  the term of the  Agreement  as  provided  in
Section 10.1 of this Agreement.

(B) Article 1 of the Agreement is amended by adding the following terms:

          1.43 Amendment - shall mean that certain  Amendment No.1,  dated on or
          about March , 2000,  by and between  the parties  hereto,  which shall
          serve as  Amendment  No.1 to this  Agreement,  which  is  incorporated
          herein by reference.

          1 .44 Amendment Effective Date - shall mean January 1, 2000.

(C) Section 3.2 of the  Agreement,  entitled  "Right of First  Offer,"  shall be
amended by adding the following sentence:

          The rights and obligations of the parties under this Section 3.2 shall
terminate as of the Amendment Effective Date.

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(D) Section 4.4 of the Agreement,  entitled  "Expansion of Territory,"  shall be
amended by adding the following sentence:

          The rights and obligations of the parties under this Section 4.4 shall
          terminate as of the Amendment Effective Date.

(E) Section 10.1 of the  Agreement,  entitled  "Term," is hereby  deleted in its
entirety, substituting in lieu thereof the following:

          10.1 Term.  This  Agreement  will commence on the Effective  Date and,
          unless sooner  terminated in  accordance  with the  provisions of this
          Agreement, will continue through and including June 31, 2000.

(F) Section 10.6.3 of the Agreement,  entitled "Marketing Rights," is deleted in
its entirety, substituting in lieu thereof the following:

          10.6.3 Marketing  Rights.  Upon termination of this Agreement,  Bard's
          rights to market and promote the Product shall  immediately  cease and
          concurrent  with or as soon as practical  following such  termination,
          Bard shall deliver to Cytogen all marketing and promotional  materials
          with respect to Product then in the  possession  of Bard or any of its
          Affiliates;  provided however, for such marketing materials related to
          Product that contain references to Bard or its Affiliates,  Bard shall
          destroy such marketing materials instead of returning them to Cytogen.
          Notwithstanding  anything to the contrary in this Section,  Bard shall
          be  entitled to retain  necessary  copies of any  marketing  materials
          related to Product for archival purposes only.

(G) A new Section 10.6.4, entitled "Transition," shall be added to the Agreement
and shall state as follows:

          10.6.4 Transition. In preparation for termination of the Agreement and
          assumption of marketing responsibilities by Cytogen, Bard shall:

                  (a) use its  reasonable  efforts prior to the  termination  of
                  this  Agreement  to  provide  a  smooth   transition  that  is
                  transparent to the urologists and nuclear medicine  physicians
                  as a result of the termination of this Agreement;

                  (b) within  forty-five  (45) days of the  termination  of this
                  Agreement,  send to Cytogen a written  report  identifying  at
                  least 250 urologist and  providing,  where known to Bard,  the
                  following information regarding each such urologist: (i) name,
                  (ii) address,  (iii) office telephone number,  and (iv) Bard's
                  perception of such urologist's opinions of ProstaScint;

                  (c)  use  its  reasonable  commercial  efforts  to  honor  all
                  outstanding commitments (by way of example only, Product Lunch
                  and Learns,  tumor boards,  and dinner meetings)  scheduled by
                  Bard through August 1, 2000; and


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                   (d)  make   reasonable   efforts   to  refer  to  a   Cytogen
                   representative  all  requests for  information  as to Product
                   received by Bard on or before December 31, 2000.

(H) Exhibit "A" of the Agreement is hereby deleted in its entirety, substituting
in lieu thereof the Exhibit "A" attached to this Amendment.

2. Other Terms. Except as otherwise provided is this Amendment,  all other terms
and conditions of the Agreement shall remain in full force and effect.

3.  Authorization.  Each  individual  executing  this  Amendment on behalf of an
entity  represents and warrants that he or she is duly authorized to execute and
deliver this Amendment on behalf of said entity;  that this Amendment is binding
on said entity,  and that this Amendment is not in violation of or  inconsistent
with or contrary to provisions of any other  agreement to which said entity is a
party.

4.  Counterparts:   Copies.  This  Amendment  may  be  signed  in  one  or  more
counterparts,  each of which will be deemed to be an  original  and all of which
when  taken  together  will  constitute  the  same  Amendment.  Any copy of this
Amendment  made by  reliable  means  shall be  considered  an  original  of this
Amendment.

IN WITNESS WHEREOF the  undersigned  have hereunto set their hand and seal as of
the date first above mentioned.


C. R. BARD, INC.                       CYTOGEN CORPORATION



By: /s/ Burt Mirsky                    By: /s/ Donald F. Crane
Name:   Burt Mirsky                    Name:   Donald F. Crane
Title:  President, BUD                 Title:  Vice President & General Counsel
Date:   04/07/00                       Date:   03/14/00















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                                   Exhibit "A"


                                   Commissions
                                   -----------

Period                                           Commission Rate
------                                           ---------------
During the first twelve                          15% of total
months following the                             Net Sales
Product Launch Date

During the Partial Year Period                   10% of that portion of
                                                 Net Sales which are less
                                                 than or equal to Baseline
                                                 Sales,1 and 26% of
                                                 Incremental Sales


Commencing with the calendar year following      10% on that portion of the Net
the Partial Year Period and continuing           Sales which are less than or
thereafter, through and  including               equal to Baseline Sales,
December 31,  1999.                              and 27%-30%2 on Incremental
                                                 Sales

January, 2000                                    9% of total Net Sales

February, 2000                                   8% of total Net Sales

March, 2000                                      7% of total Net Sales

April, 2000                                      6% of total Net Sales

May, 2000                                        5% of total Net Sales

June, 2000                                       4% of total Net Sales

---------------------

1.        During the Partial  Year Period  only,  Baseline  Sales shall mean the
          amount of Net Sales achieved during the preceding  twelve month period
          multiplied by a fraction, the numerator of which is the number of days
          in this period and the  denominator  of which is 365. For example,  if
          the  Baseline  Sales  for the first 12 months  following  the  Product
          Launch Date was $10  million  and the Product  Launch Date was January
          31, 1997, the Baseline Sales for the Partial Year Period only would be
          equal to $9,150,000 (10 million x 334/365).

2.        During the first calendar year following the Partial Year Period,  the
          Commission  Rate  for  Incremental  Sales  shall  be 27% and it  shall
          increase  by one (1)  percentage  point each year  therefore  until it
          reaches the level of 30% at which time it shall remain constant.