EXHIBIT 5.1


                                 LAW OFFICES OF
                            DECHERT PRICE & RHOADS

                        Princeton Pike Corporate Center
                                 P.O. Box 5218
                            Princeton, NJ 08543-5218

                            Telephone: (609)620-3200
                               Fax: (609)620-3259





                                        June 9, 2000



CYTOGEN  CORPORATION
600 College Road East CN 5308
Princeton,  NJ
08540-5308

          Re: Registration Statement on Form S-3; File No. 333-33436
              ------------------------------------------------------

Ladies and Gentlemen:

     We have acted as counsel to Cytogen Corporation, a Delaware
corporation (the "Company"), in connection with the preparation and filing of a
registration statement on Form S-3, File No. 333-33436, originally filed on
March 28, 2000 with the Securities and Exchange Commission (the "Commission")
and as amended by Amendment No. 1 thereto being filed with the Commission on the
date hereof (as so amended, the "Registration Statement"), in connection with
the registration under the Securities Act of 1933, as amended, (the "Securities
Act") of a shelf offering of up to 6,000,000 shares of the Company's Common
Stock, par value $.01 per share (the "Shares"), all of which are authorized but
heretofore unissued.

     We have participated in the preparation of the Registration
Statement  and have made such legal and  factual  examination  and inquiry as we
have  deemed  necessary  for  the  rendering  of this  opinion.  In  making  our
examination we have assumed the genuineness of all signatures,  the authenticity
of  all  documents  submitted  to us as  originals  and  the  conformity  to all
authentic original documents of all documents  submitted to us as copies.


     Based upon the foregoing, it is our opinion, that when (i) issued,
delivered and paid for in the manner described in the Registration Statement
assuming: (a) that at least par value will be paid for the Shares and (b) the
completion of all proceedings to be taken in order to permit such issuances to
be carried out in accordance with applicable securities laws; and (ii)
certificates representing the Shares in the form of the specimen certificate
examined by us have been manually signed by an authorized officer of the
transfer agent and registrar for the Common  Stock and  registered  by such



CYTOGEN CORPORATION
June 9, 2000
Page 2


transfer agent and registrar, the issuance and sale of the Shares will have been
duly authorized, and the Shares will be legally and validly issued, fully paid
and nonassessable.


     We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to the use of our name in the Prospectus contained
therein, under the caption "Legal Matters." In giving such consent we do not
thereby admit that we are in the category of persons whose consent is required
under Section 7 of the Securities Act.

                                        Very truly yours,

                                        /s/ Dechert Price & Rhoads