[LETTERHEAD FOR DAVIS WRIGHT TREMAINE LLP]
                                  LAW OFFICES

                                October 3, 1997


                                                                    Underwritten
                                                                    ------------

Cell Therapeutics, Inc.
201 Elliott Avenue West
Suite 400
Seattle, WA 98119

        Re:     Cell Therapeutics, Inc.
                Registration Statement on Form S-3 (No. 333-36603)

Ladies and Gentlemen:

        We have examined the above-referenced Registration Statement on Form S-3
filed by Cell Therapeutics, Inc., a Washington corporation (the "Company"), with
the Securities and Exchange Commission on September 29, 1997 (as such may 
thereafter be amended or supplemented, the "Underwritten Registration 
Statement"), in connection with the registration under the Securities Act of 
1933, as amended, of up to 2,300,000 shares of Common Stock (the "Shares") of 
the Company. We understand that the Shares are to be sold to the underwriters of
the offering for resale to the public as described in the Registration 
Statement.

        As special local Washington counsel for the Company and in connection 
with the opinions expressed below, we have examined copies of (a) the 
Registration Statement and (b) the originals, or copies identified to our 
satisfaction, of such corporate records of the Company, certificates of public 
officials, officers of the Company and other persons, and such other documents, 
agreements and instruments as we have deemed necessary as a basis for the 
opinions hereinafter expressed. In our examinations, we have assumed the 
genuineness of all signatures, the authenticity of all documents submitted to us
as originals and the conformity with the originals of all documents submitted to
us as copies. In expressing the opinions set forth below, we have also relied on
certain certificates of officers of the Company and certificates of public 
officials.

        Our opinions expressed below are limited to the laws of the State of 
Washington, if any.

        Based on such examination and subject to the foregoing, we are of the
opinion that, upon completion of the proceedings being taken or contemplated to
be taken prior to the issuance of the Shares, and the proceedings being taken in
order to permit the offering described in the Registration Statement to be
carried out in accordance with applicable state securities laws, the Shares,
when issued and sold in the manner described in the Registration Statement and
in
        

 
Cell Therapeutics, Inc.
October 3, 1997
Page 2

accordance with the resolutions adopted by the Board of Directors of the
Company, will be legally and validly issued, fully paid and nonassessable.

        We consent to the use of this opinion as an exhibit to the Registration 
Statement and further consent to the use of our name wherever appearing in the 
Registration Statement, including the Prospectus constituting a part thereof, 
and any amendments thereto.

                                                Very truly yours,

                                                Davis Wright Tremaine LLP