<PAGE>
 
                      SECURITIES AND EXCHANGE COMMISSION
                            WASHINGTON, D.C. 20549

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

                                   FORM 8-K

                                CURRENT REPORT
                    PURSUANT TO SECTION 13 OR 15(d) OF THE
                        SECURITIES EXCHANGE ACT OF 1934

                              September 25, 1996
               Date of Report (Date of earliest event reported)

                            CELL THERAPEUTICS, INC.
            (Exact name of registrant as specified in its charter)

         WASHINGTON                    0-28386                91-1533912
(State or Other Jurisdiction   (Commission File Number)     (IRS Employer 
     of Incorporation)                                    Identification No.)

                           201 Elliott Avenue, West
                           Seattle, Washington 98119
         (Address of principal executive offices, including zip code)

                                (206) 282-7100
             (Registrant's telephone number, including area code)

                                Not applicable
         (Former name or former address, if changed since last report)


<PAGE>
 
                                       2


ITEM 5.   OTHER EVENTS.

NOTICE OF UNREGISTERED OFFERING

          On September 25, 1996 Cell Therapeutics, Inc. (the "Company") issued a
press release under Securities and Exchange Commission Rule 135c giving notice
of the closing of an unregistered private offering of 44,776.119 shares of its
Series A Convertible Preferred Stock, for an aggregate purchase price of
$15,000,000. The text of that press release is included with this report as
Exhibit 99.1.



ITEM 7.   FINANCIAL STATEMENTS, PRO FORMA FINANCIAL INFORMATION AND EXHIBITS.

          (c)  Exhibits

<TABLE> 
<CAPTION> 

    Exhibit No.                             Description
    -----------                             -----------
    <C>                       <S>
        99.1                  Press release dated September 25, 1996 issued 
                              under Securities and Exchange Commission Rule 135c
                              giving notice of the closing of an unregistered 
                              offering of Series A Covertible Preferred Stock.

</TABLE>
 

<PAGE>
 
                                       3


                                  SIGNATURES

     Pursuant to the requirements of the Securities Exchange Act of 1934, the 
Registrant has duly caused this report to be signed on its behalf by the 
undersigned hereunto duly authorized.

                                       CELL THERAPEUTICS, INC.


Dated: September 25, 1996              By /s/ JAMES A. BIANCO, M.D.
                 --                       -------------------------------------
                                          James A. Bianco, M.D.
                                          President and Chief Executive Officer


<PAGE>
 

                                 EXHIBIT INDEX

<TABLE> 
<CAPTION> 

Exhibit No.                      Description                           Page No.
- -----------                      -----------                           --------
<C>                  <S>                                               <C>

   99.1              Press release dated September 25, 1996 issued
                     under Securities and Exchange Commission Rule
                     135c giving notice of the closing of an 
                     unregistered offering of Series A Convertible
                     Preferred Stock.
</TABLE>
 





<PAGE>
 
                                                                    EXHIBIT 99.1

                              [LETTERHEAD OF CTI]


FOR IMMEDIATE RELEASE                     Contact: Lee M. Parker, Vice President
                                          -------
                                                         Cell Therapeutics, Inc.
                                                                    206/282-7100
                                                          lparker@ctiseattle.com

                 CELL THERAPEUTICS RAISES $15 MILLION THROUGH
                               PRIVATE PLACEMENT

SEATTLE--September 25, 1996--Cell Therapeutics (cti) today announced a 
company-managed private placement of $15 million of Series A Convertible 
Preferred Stock with existing institutional and accredited individual 
investors. These securities have not been registered under the Securities Act of
1933 and may not be offered or sold in the United States without registration or
applicable exemption from registration requirements.

Cell Therapeutics President and CEO James A. Bianco, MD, stated: "In light of 
capital market conditions for biotechnology-companies, we felt it prudent to 
secure enough additional private capital so that, combined with our existing 
funds, we would be able to carry forward company operations through 1997."

Cell Therapeutics, Inc. is a Seattle-based biopharmaceutical company focusing on
the development of a new class of drugs that seeks to selectively regulate the 
metabolism of phospholipids in intracellular signaling pathways relevant to 
cancer and
 immune and inflammatory diseases.