Exhibit 5.1
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  April 10, 1998
  
  Cytogen Corporation
  600 College Road East
  Princeton, New Jersey 08540
  
  Ladies and Gentlemen:
  
          We have acted as counsel to Cytogen Corporation, a
  Delaware corporation (the "Company"), in connection with the
  preparation and filing by the Company of a Registration
  Statement on Form S-3 (the "Registration Statement") under the
  Securities Act of 1933, as amended (the "Act"), for the
  registration of 6,250,000 shares of common stock, $.01 par
  value per share (the "Common Stock"), of the Company which may
  be issued upon the conversion of the Company's 6% Convertible
  Preferred Stock, Series B (the "Series B Preferred Stock"),
  plus such additional indeterminate number of shares of Common
  Stock as may become issuable either as a result of the          
  anti-dilution provisions of the Certificate of Designation 
  of the Series B Preferred Stock (the "Certificate 
  of Designation")pursuant to which the Common Stock will 
  be issued, or by reason of a reduction in the conversion price 
  of the Series B Preferred Stock in accordance with the provisions 
  of the Certificate of Designation.
  
          We have examined and are familiar with originals or
  copies, certified or otherwise identified to our satisfaction,
  of such documents, corporate records, certificates of public
  officials and officers of the Company and such other
  instruments as we have deemed necessary or appropriate as a
  basis for the opinions expressed below, including the
  Registration Statement, the Restated Certificate of
  Incorporation of the Company and the By-laws of the Company.
  
          Based on the foregoing, we are of the opinion that
  the Common Stock issuable upon conversion of the Series B
  Preferred Stock (including those shares of Series B Preferred
  Stock issued as dividends, if any) has been duly authorized and
  reserved for issuance and, when duly issued and delivered upon
  conversion of the Series B Preferred Stock in accordance with
  the terms of the Convertible Preferred Stock Purchase Agreement
  dated December 9, 1997 and the Certificate of Designation, will
  be validly issued, fully paid and nonassessable. 


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          We hereby consent to the filing of this opinion as
  Exhibit 5.1 to the Registration Statement.  In giving such
  consent, we do not thereby admit that we come within the
  category of persons whose consent is required under Section 7
  of the Act or the rules and regulations of the Securities and
  Exchange Commission thereunder. 
  
          We express no opinion as to the laws of any
  jurisdiction other than the laws of the State of New York, the
  general corporate laws of the State of Delaware and the federal
  law of the United States of America.  The foregoing opinion is
  rendered as of the date hereof, and we assume no obligation to
  update such opinion to reflect any facts or circumstances which
  may hereafter come to our attention or any changes in the law
  which may hereafter occur.
  
                                Very truly yours,
                                
                                /s/ DEWEY BALLANTINE LLP
                                
                                DEWEY BALLANTINE LLP


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