1
 
   
                          [COOLEY GODWARD LETTERHEAD]
    
 
   
October 8, 1997
    
 
   
Coulter Pharmaceutical, Inc.
    
   
550 California Avenue, Suite 200
    
   
Palo Alto, California 94306-1440
    
 
   
Ladies and Gentlemen:
    
 
   
     You have requested our opinion with respect to certain matters in
connection with the filing by Coulter Pharmaceutical, Inc. (the "Company") of a
Registration Statement on Form S-1 on September 29, 1997, as amended (the
"Registration Statement") with the Securities and Exchange Commission covering
the offering of up to Two Million Seven Hundred Sixty Thousand (2,760,000)
shares of the Company's Common Stock, $.001 par value (the "Shares").
    
 
   
     In connection with this opinion, we have examined the Registration
Statement and related Prospectus, your Restated Certificate of Incorporation and
Bylaws, as amended, and such other documents, records, certificates, memoranda
and other instruments as we deem necessary as a basis for this opinion. We have
assumed the genuineness and authenticity of all documents submitted to us as
originals, the conformity to originals of all documents submitted to us as
copies thereof, and the due execution and delivery of all documents where due
execution and delivery are a prerequisite to the effectiveness thereof.
    
 
   
     On the basis of the foregoing, and in reliance thereon, we are of the
opinion that the Shares, when sold and issued in accordance with the
Registration Statement and related Prospectus, will be validly issued, fully
paid, and nonassessable.
    
 
   
     We consent to the filing of this opinion as an exhibit to the Registration
Statement.
    
 
   
                                          Very truly yours,
    
 
   
                                          Cooley Godward LLP
    
 
   
                                          /s/ JAMES C. KITCH
    
 
   
                                          James C. Kitch