<PAGE>

                                                                     EXHIBIT 4.1


                          SECURITIES PURCHASE AGREEMENT


         This Securities Purchase Agreement (the "Agreement") is entered into as
of February 15, 2000 (the "Execution Date"), between Cell Therapeutics, Inc., a
Washington corporation (the "Company"), and the investors set forth on the
signature page hereto (each an "Investor" and collectively the "Investors").

WHEREAS:

         The Company and the Investors are executing and delivering this
Agreement in reliance upon the exemption from securities registration afforded
by Rule 506 under Regulation D ("Regulation D") as promulgated by the United
States Securities and Exchange Commission (the "SEC") under the Securities Act
of 1933, as amended (the "1933 Act");

         The Company desires to issue and sell to each Investor and each
Investor desires to purchase the number of shares of common stock, no par value
per share (the "Common Stock") set forth opposite such Investor's name on
Exhibit A attached hereto, with each share having a purchase price of Twelve
Dollars ($12.00); and

         Contemporaneous with the execution and delivery of this Agreement, the
parties hereto are executing and delivering a Registration Rights Agreement, in
the form attached hereto as Exhibit B (the "Registration Rights Agreement"),
providing for the registration of the Shares (as herein defined).

         NOW THEREFORE, the Company and Investor hereby agree as follows:

I. PURCHASE AND SALE OF SECURITIES.

         (a) Sale of Common Stock. Subject to the terms and conditions hereof,
             --------------------
the Company shall issue and sell to each Investor and each Investor agrees to
purchase from the Company, the number of shares of Common Stock set forth
opposite such Investor's name on Exhibit A (collectively, together with any
Common Stock issued in replacement thereof or as a dividend thereon or otherwise
with respect thereto in accordance with the terms thereof, the "Shares") each
with a purchase price of Twelve Dollars ($12.00) per share (the "Purchase
Price"). One (1) Share will be issued to each Investor for each $12.00 provided
by the Investor to the Company.

         (b) Closing. Subject to the terms set forth in this Agreement, the
             -------
issuance, sale and purchase of the Common Stock shall be consummated in a single
closing (the "Closing").

         (c) Payment. At the Closing each Investor shall pay the Purchase Price
             -------
for the Shares being acquired by it by wire transfer to "State Street Bank &
Trust Company, N.A., "Escrow Agent," F/B/O Cell Therapeutics, Inc.", in
accordance with the Company's written wiring instructions, against delivery of
the appropriate amount of duly executed stock certificates and the items
required by Section 7 for the same and the Company shall deliver such Shares
against delivery of such Purchase Price.

                                  Page 1 of 15
<PAGE>

         (d) Closing Date. Subject to the satisfaction of the conditions set
             ------------
forth in Sections 6 and 7 below, the date and time of the issuance, sale and
purchase of Shares pursuant to this Agreement shall be February 22, 2000 or such
other date as the Company and the Investor may mutually agree. Each Closing
shall occur at 9:30 p.m. local time, at the offices of the Company. The date of
a Closing hereunder is hereinafter referred to as a "Closing Date."


II. INVESTOR'S REPRESENTATIONS AND WARRANTIES. Each Investor, severally, and not
jointly, represents and warrants to the Company that, as of the date hereof:

         (a) Investment Purpose. Such Investor is purchasing the Shares for its
             ------------------
own account as principal for investment only and not with a present view towards
the public sale or distribution thereof, except pursuant to sales registered or
exempted from registration under the 1933 Act. By making this representation,
such Investor does not represent that it will hold such Shares for any period of
time.

         (b) Accredited Investor Status. Such Investor is an "accredited
             --------------------------
investor" as that term is defined in Rule 501(a) of Regulation D and has such
business and financial experience as is required to give it the capacity to
protect its own interests in connection with the purchase of the Shares. The
Company has completed the Investor Questionnaire (the "Investor Questionnaire")
attached hereto as Exhibit C, and the information contained therein is accurate.

         (c) Prior Investment Experience. The Investor hereby acknowledges and
             ---------------------------
represents that (i) the Investor has prior investment experience, including
investment in Shares which are non-listed, unregistered and/or not traded on the
Nasdaq National or SmallCap Market, a national stock exchange nor on the NASD's
automated quotation system for actively traded stocks, or the Investor has
employed the services of an investment advisor, attorney and/or accountant to
read all of the documents furnished or made available by the Company to the
Investor and to all other prospective investors in the Shares and to evaluate
the merits and risks of such an investment on the Investor's behalf; (ii) the
Investor recognizes the highly speculative nature of this investment; and (iii)
the Investor is able to bear the economic risk which the Investor hereby
assumes. The Investor hereby represents that the Investor, either by reason of
the Investor's business or financial experience or the business or financial
experience of the Investor's professional advisors, has the capacity to protect
the Investor's own interests in connection with the transaction contemplated
hereby.

         (d) Reliance on Exemptions. Such Investor understands that the Shares
             ----------------------
are being offered and sold to it in reliance upon Rule 506 of Regulation D of
the 1933 Act as a specific exemption from the registration requirements of
United States federal and state securities laws and that the Company is relying
upon the truth and accuracy of, and the Investor's compliance with, the
representations, warranties, agreements, covenants, acknowledgments and
understandings of the Investor set forth herein in order to determine the
availability of such exemptions and the eligibility of the Investor to acquire
the Shares.

                                  Page 2 of 15
<PAGE>

         (e) Acknowledgement of Risks. The Investor recognizes that the purchase
             ------------------------
of Shares involves a high degree of risk including, but not limited to, the
following: (i) the Company remains a development stage business with limited
operating history and requires substantial funds in addition to the proceeds of
the Offering; (ii) an investment in the Company is highly speculative, and only
investors who can afford the loss of their entire investment should consider
investing in the Company and the Shares; (iii) the Investor may not be able to
liquidate his/its investment; (iv) transferability of the Common Stock is
extremely limited; (v) in the event of a disposition of the Common Stock, the
Investor could sustain the loss of his/its entire investment and (vi) the
Company has not paid any dividends on its Common Stock since inception and does
not anticipate the payment of dividends in the foreseeable future.

         (f) Information. Such Investor and its advisors, if any, have been
             -----------
furnished with all materials relating to the business, finances and operations
of the Company and materials relating to the offer and sale of the Securities
which have been requested by such Investor or its advisors. Such Investor and
its advisors, if any, have been afforded the opportunity to ask questions of the
Company and have received what such Investor believes to be satisfactory answers
to any such inquiries. Neither such inquiries nor any other due diligence
investigation conducted by such Investor or any of its advisors or
representatives shall modify, amend or affect such Investor's right to rely on
the Company's representations and warranties contained in Section 3 below. Such
Investor understands that its investment in the Shares involves a significant
degree of risk.

         (g) Governmental Review. Such Investor understands that no United
             -------------------
States federal or state agency or any other government or governmental agency
has passed upon or made any recommendation or endorsement of the Shares.

         (h) Transfer or Resale. Such Investor understands that (i) except as
             ------------------
provided in the Registration Rights Agreement, the Shares have not been and are
not being registered under the 1933 Act or any applicable state securities laws,
and may not be transferred unless (1) subsequently included in an effective
registration statement thereunder, (2) the Investor shall have delivered to the
Company an opinion of counsel (which opinion shall be reasonably satisfactory to
the Company) to the effect that the Shares to be sold or transferred may be sold
or transferred pursuant to an exemption from such registration or (3) sold
pursuant to Rule 144 promulgated under the 1933 Act (or a successor rule) ("Rule
144")), (ii) any sale of such Shares made in reliance on Rule 144 may be made
only in accordance with the terms of said Rule and further, if Rule 144 is not
applicable, any resale of such Shares under circumstances in which the seller
(or the person through whom the sale is made) may be deemed to be an underwriter
(as that term is defined in the 1933 Act) may require compliance with some other
exemption under the 1933 Act or the rules and regulations of the "SEC"
thereunder, and (iii) neither the Company nor any other person is under any
obligation to register such Shares under the 1933 Act or any state securities
laws or to comply with the terms and conditions of any exemption thereunder (in
each case, other than pursuant to the Registration Rights Agreement).

         (i) Legends. Such Investor understands that until such time as the
             -------
Shares have been registered under the 1933 Act as contemplated by the
Registration Rights Agreement, the Shares

                                  Page 3 of 15
<PAGE>

may bear a restrictive legend in substantially the following form (and a stop-
transfer order may be placed against transfer of the certificates for such
Shares):

           (i)   The following legend under the 1933 Act:

                 "THE SECURITIES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED
                 UNDER THE UNITED STATES SECURITIES ACT OF 1933, AS AMENDED (THE
                 "ACT"), AND MAY NOT BE OFFERED, SOLD, TRANSFERRED, ASSIGNED,
                 PLEDGED OR HYPOTHECATED ABSENT AN EFFECTIVE REGISTRATION
                 THEREOF UNDER SUCH ACT OR COMPLIANCE WITH RULE 144 PROMULGATED
                 UNDER SUCH ACT, OR UNLESS THE COMPANY HAS RECEIVED AN OPINION
                 OF COUNSEL, REASONABLY SATISFACTORY TO THE COMPANY AND ITS
                 COUNSEL, THAT SUCH REGISTRATION IS NOT REQUIRED";

           (ii)  The Shares shall not contain the legend set forth above at any
     time while a registration statement filed pursuant to the Registration
     Rights Agreement is effective under the 1933 Act or, in the event there is
     not such an effective registration statement, at such time, in the opinion
     of counsel to the Company, such legend is not required under applicable
     requirements of the 1933 Act (including judicial interpretations and
     pronouncements issued by the staff of the SEC). The Company agrees that, in
     the event any Shares are issued with a legend in accordance with this
     Section 2(i)(2), it will, within three (3) trading days after request
     therefor by such Investor, provide such Investor with a certificate or
     certificates representing such Shares, free from such legend at such time
     as such legend would not have been required under this Section 2(h)(2) had
     such issuance occurred on the date of such request. The Company may not
     make any notation on its records or give instructions to any transfer agent
     of the Company which enlarge the restrictions of transfer set forth in this
     Section.

     (i)   Authorization; Enforcement. Such Investor represents and warrants
           --------------------------
to the Company that (i) such Investor has all requisite legal and corporate or
other power and capacity and has taken all requisite corporate or other action
to execute and deliver this Agreement, to purchase the Shares to be purchased by
it and to carry out and perform all of its obligations under this Agreement, and
(ii) this Agreement constitutes the legal, valid and binding obligation of the
Investor, enforceable in accordance with its terms, except (1) as limited by
applicable bankruptcy, insolvency, reorganization, or similar laws relating to
or affecting the enforcement of creditors' rights generally and (2) as limited
by equitable principles generally and (iii) to the extent that indemnification
provisions in the Registration Rights Agreement may be limited by applicable
federal or state securities laws.

     (j)   No Legal, Tax or Investment Advice. Such Investor understands that
           ----------------------------------
nothing in this Agreement or any other materials presented to the Investor in
connection with the purchase and sale of the Shares constitutes legal, tax or
investment advice. Such Investor has consulted such legal, tax and investment
advisors as it, in its sole discretion, has deemed necessary or

                                  Page 4 of 15
<PAGE>

appropriate in connection with this Agreement and all exhibits hereto and the
transactions contemplated herein and therein.

     (k)   Residency. Such Investor is a company organized under the laws of the
           ---------
jurisdiction set forth opposite such Investor's name on it's the signature page.


III. REPRESENTATIONS AND WARRANTIES OF THE COMPANY. The Company represents and
     ---------------------------------------------
warrants to the Investor that, except as set forth in the Schedule of Exceptions
attached hereto as Exhibit D, as of the date hereof:

     (a)   Organization and Qualification. The Company is duly organized,
           ------------------------------
validly existing and in good standing under the laws of Washington, with
requisite corporate power and authority to own, lease and operate its properties
and to carry on its business as presently conducted and/or proposed to be
conducted. The Company and each of its subsidiaries is qualified to do business
as a foreign corporation in each jurisdiction in which the ownership of its
property or the nature of its business requires such qualification, except where
failure to so qualify would not have an Adverse Effect. For purposes of this
Agreement, "Adverse Effect" means with respect to the Company and its
subsidiaries, taken as a whole, any event, change or effect that, when taken
individually or together with all other adverse changes and effects, is or is
reasonably likely to be materially adverse to the condition (financial or
otherwise), properties, assets, liabilities, business, operations or results of
operations of the Company and its subsidiaries taken as a whole or impair the
ability of the Company to perform fully on a timely basis its obligations under
the Transaction Documents. "Transaction Documents" means, collectively, this
Agreement, the Registration Rights Agreement, and the Investor Questionnaire.

     (b)   Authorization; Enforcement. The Company has all requisite legal and
           --------------------------
corporate power and has taken all requisite corporate action to execute and
deliver this Agreement and the Registration Rights Agreement to sell and issue
the Shares and to carry out and perform all of its obligations under the
Transaction Documents. All corporate action on the part of the Company, its
directors and stockholders necessary for the authorization, execution, delivery
and performance of this Agreement and the Registration Rights Agreement by the
Company, and the authorization, sale, issuance and delivery of the Shares and
the performance of the Company's obligations under the Transaction Documents has
been taken. Each of the Transaction Documents constitutes the legal, valid and
binding obligations of the Company, enforceable in accordance with their
respective terms, except (i) as limited by applicable bankruptcy, insolvency,
reorganization or similar laws relating to or affecting the enforcement of
creditors' rights generally, (ii) as limited by equitable principles generally
and (iii) to the extent that indemnification provisions in the Registration
Rights Agreement may be limited by applicable federal or state securities laws.

     (c) Capitalization. [TO BE PROVIDED BY CTIC] The authorized capital
         --------------
stock of the Company consists of 100,000,000 shares of common stock, no par
value per share, of which there were 17,758,838 shares issued and outstanding as
of January 31, 2000, and 10,000,000 shares of Preferred Stock, $0.01 par value
per share, 10,000 of which shares have been designated as Series A Preferred
Stock and are issued and outstanding. All outstanding shares of

                                  Page 5 of 15
<PAGE>

Common Stock and Preferred Stock are duly authorized, validly issued, fully paid
and nonassessable, free of any liens or encumbrances and are not subject to
preemptive rights. As of January 31, 2000, the Company had reserved 3,836,715
shares of Common Stock for issuance to employees, directors and consultants
pursuant to the 1994 Amended and Restated CTI Stock Option Plan, of which
233,752 shares have been issued pursuant to option exercises, and 2,994,318
shares of Common Stock are subject to outstanding, unexercised options. As of
September 17, 1999, the Company had reserved 285,714 shares of Common Stock for
issuance to employees pursuant to the 1996 CTI Employee Stock Purchase Plan
(together with the Stock Option Plan, the ("CTI Plans"), of which 151,780 shares
have been issued to employees. Other than as set forth in the Schedule of
Exceptions, the CTI Plans, the SEC Documents or as contemplated in this
Agreement, there are no other options, warrants, calls, rights, commitments or
agreements of any character to which the Company is a party or by which either
the Company is bound or obligating the Company to issue, deliver, sell,
repurchase or redeem, or cause to be issued, delivered, sold, repurchased or
redeemed, any shares of the capital stock of the Company or obligating the
Company to grant, extend or enter into any such option, warrant, call, right,
commitment or agreement.

     (d)   Issuance of Shares. The Shares are duly authorized and, upon
           ------------------
issuance in accordance with the terms of this Agreement, will be validly issued,
fully paid and non-assessable, and free from all taxes, liens and charges with
respect to the issue thereof and shall not be subject to preemptive rights or
other similar rights of stockholders of the Company. Based in part upon the
representations of the Investor in this Agreement, the offer, sale and issuance
of the Common Stock will be made in compliance with all applicable federal and
state securities laws.

     (e)   No Conflicts. The execution, delivery and performance of the
           ------------
Transaction Documents by the Company and the consummation by the Company of the
transactions contemplated hereby and thereby do not and will not (i) conflict
with or result in a violation of any provision of the Company's Certificate of
Incorporation or Bylaws or (ii) violate or conflict with, or result in a breach
of any provision of, or constitute a default (or an event which with notice or
lapse of time or both would become a default) under, or give to others any
rights of termination, acceleration or cancellation of (with or without notice,
lapse of time or both), any indenture, mortgage, lease or other agreement or
instrument, or result in a violation of any law, rule, regulation, order,
judgment or decree (including federal and state securities laws and regulations)
applicable to the Company or by which any property or asset of the Company is
bound or affected (in each case except for such conflicts, defaults,
terminations, accelerations, cancellations and violations that are not
reasonably likely to, individually or in the aggregate, have an Adverse Effect).

     (f)   Accuracy of Reports; Financial Statements. All reports required to
           -----------------------------------------
be filed with the SEC by the Company during the twelve (12) month period
preceding the date hereof under the Securities Exchange Act of 1934, as amended
(the "Exchange Act") (the "SEC Documents"), have been duly and timely filed,
were in substantial compliance with the requirements of the 1933 Act and
Exchange Act when filed, were complete and correct in all material respects as
of the dates at which the information was furnished, and contained (as of such
dates) no untrue statement of a material fact nor omitted to state a material
fact necessary in order to make the

                                  Page 6 of 15
<PAGE>

statements made therein in light of the circumstances in which made not
misleading. The financial statements of the Company included in the SEC
Documents (the "Financial Statements") comply in all material respects with
applicable accounting requirements and with the published rules and regulations
of the SEC with respect thereto. The Financial Statements have been prepared in
accordance with generally accepted accounting principles ("GAAP") consistently
applied and fairly present the consolidated financial position of the Company
and any subsidiaries at the dates thereof and the consolidated results of
operations and consolidated cash flows for the periods then ended (subject, in
the case of unaudited statements, to normal, recurring year-end adjustments).
Except as set forth in the SEC Documents, the Company does not have any
liabilities or obligations of any nature (whether accrued, absolute, contingent
or otherwise) required by GAAP to be set forth on a balance sheet of the Company
or in the notes thereto.

     (g)   Changes. Since September 30, 1999, there has not been (a) any
           -------
incurrence by the Company of any material liability, absolute or contingent, or
(b) any event or condition of any character that has materially and adversely
affected or might materially and adversely affect the business, properties,
prospects or financial condition of the Company (as such business is presently
conducted and as it is proposed to be conducted). There is no material liability
or contingency of the Company that is not disclosed in the SEC Documents.
[SHOULD INCLUDE POLARX ON THE SCHEDULE OF EXCEPTIONS.]

     (h)   Governmental Consents, etc. No consent, approval or authorization of
           --------------------------
or designation, declaration or filing with any governmental authority on the
part of the Company is required in connection with the valid execution, delivery
and performance of the Transaction Documents, or the consummation of any other
transaction contemplated hereby and thereby, except such filings as may be
required to be made with the SEC, the National Association of Securities
Dealers, Inc. ("NASD") the Nasdaq National Market (the "NADDAQ"), such filings
as may be required under the Hart-Scott-Rodino Antitrust Improvements Act of
1976, as amended ("HSR") and filings with governmental authorities for purposes
of effecting compliance with the securities and blue sky laws in the states in
which Shares are offered and/or sold, which compliance will be effected in
accordance with such laws. The Company has not received any delisting notices,
notice of violation or similar inquiry regarding its eligibility for listing
from the NASDAQ.

     (i)   Litigation. There is no pending or, to the best of the Company's
           ----------
knowledge, threatened lawsuit, administrative proceeding, arbitration, labor
dispute or governmental investigation ("Litigation") to which the Company is a
party or by which any material portion of its assets, taken as a whole, may be
bound, nor is the Company aware of any basis therefor, which Litigation, if
adversely determined, would have an Adverse Effect.

     (j)   Patents and Trademarks. To its knowledge, except as disclosed in the
           ----------------------
SEC Documents, the Company owns or possesses the right to use to all patents,
trademarks, service marks, tradenames, copyrights, trade secrets, licenses,
information and proprietary rights and processes necessary for its business as
now conducted and as proposed to be conducted, without infringement of any
rights of a third party. Except as is disclosed in the SEC Documents, the
Company has not received any communications alleging that the Company has
violated or, by

                                  Page 7 of 15
<PAGE>

conducting its business as proposed, would violate any of the patents,
trademarks, service marks, tradenames, copyrights, trade secrets or other
proprietary rights or processes of any other person or entity, which violation
would have an Adverse Effect on the Company. Except as disclosed in the SEC
Documents, the Company has not granted (nor has the Company licensed from a
third party) any material rights to or licenses to its patents, trademarks,
service marks, tradenames, copyrights, trade secrets or other proprietary rights
or processes.

     (k)   Registration Rights. Except for the registration rights granted in
           -------------------
connection with the (i) license of PG-Taxol; (ii) the acquisition of PolaRx
BioPharmaceuticals, Inc.; and (iii) the sale of the Series A Preferred Stock,
there are no outstanding obligations of the Company to register the securities
of a third party.

     (l)   Disclosure. No representation or warranty of the Company contained
           ----------
in any Transaction Documents or the exhibits attached thereto, contains any
untrue statement of a material fact or omits to state a material fact necessary
in order to make the statements contained herein or therein in light of the
circumstances under which they were made not misleading. The Company confirms
that it has not provided the Investors or their agents or counsel with any
information that constitutes or might constitute material non-public
information. The Company understands and confirms that the Investors shall be
relying on the foregoing representations in effecting transactions in securities
of the Company.

     (m)   Solvency; No Default. The Company has sufficient funds and cash flow
           --------------------
to pay its debts and other liabilities as they become due, and the Company is
not in default with respect to any material debt or liability.

     (n)   No Default or Violation. Neither the Company nor any subsidiary is in
           -----------------------
violation of or default under any provision of (and no event has occurred which
has not been waived which, with notice or lapse of time or both, would result in
a default by the Company or any subsidiary), nor has the Company or any
subsidiary received notice of a claim that it is in default under or that it is
in violation of (a) its Certificate of Incorporation or Bylaws, or (b) any
mortgage, indenture, lease or other agreement or instrument, permit, concession,
franchise or license to which it is a party or by which it is bound or (c) any
federal or state judgment, order, decree, statute, law, ordinance, rule or
regulation applicable to the Company, except with respect to clauses (b) and (c)
above, such violations or defaults as would not have an Adverse Effect.

     (o)   Eligibility. The Company is eligible and meets the requirements to
           -----------
register for resale on Form S-3 under the 1933 Act.


IV.  COVENANTS.

     (a)   Best Efforts. The parties shall use their commercially reasonable
           ------------
best efforts to satisfy timely each of the conditions described in Section 6 and
Section 7 of this Agreement.

     (b)   Form D; Blue Sky Laws. The Company agrees to file a Form D with
           ---------------------
respect to the Shares as required under Regulation D and to provide a copy
thereof to the Investors promptly after such filing. The Company shall qualify
the Shares for sale to the Investors

                                  Page 8 of 15
<PAGE>

pursuant to this Agreement under applicable securities or "blue sky" laws of the
states of the United States (or to obtain an exemption from such qualification),
and shall provide evidence of any such action so taken to Investor.

     (c)   Listing. The Company shall, no later than fourteen (14) business days
           -------
after the Closing Date, secure the listing of the Underlying Shares upon the
NASDAQ and each national securities exchange or automated quotation system, if
any, upon which the shares of Common Stock are then listed (subject to official
notice of issuance) and shall maintain, so long as any other shares of Common
Stock shall be so listed, such listing of all such Underlying Shares. The
Company will obtain and maintain the listing and trading of its Common Stock on
the NASDAQ, the Nasdaq SmallCap Market, the New York Stock Exchange, or the
American Stock Exchange as may then be applicable, and will comply in all
material respects with the Company's reporting, filing and other obligations
under the bylaws or rules of the NASD.

     (d)   Transfer of Shares by Investor.
           ------------------------------

           (i)  As set forth in this Section 4(i), each Investor shall have
     limited rights to transfer the Shares before they are registered under the
     1933 Act or transferable under Rule 144. Once the Shares are registered
     under the 1933 Act or transferable under Rule 144, each Investor may
     transfer the Shares as permitted by federal and state securities laws.
     Prior to such time, each Investor may transfer the Shares solely to (A) an
     Affiliate of the Investor (as such term is defined in Rule 405 under the
     1933 Act), (B) an entity solely in connection with charitable contributions
     by the Investor or (C) an individual or entity solely for estate planning
     purposes, provided that written notice is provided to the Company five (5)
     business days prior to any such assignment and immediately following such
     assignment the further disposition of such Shares by the transferee or
     assignee is restricted under the 1933 Act and the transferee or assignee
     agrees in writing to be bound by all of the provisions of this Agreement.
     All other transfers of the Shares are prohibited unless such Investor has
     obtained the Company's prior written consent.

           (ii)  At least five (5) business days prior to the date it intends to
     transfer Shares in a private transaction, an Investor shall deliver to the
     Company a written notice (the "Transfer Notice") stating: (A) the
     Investor's bona fide intention to sell or otherwise transfer the Shares;
     (B) the name and address of each permitted proposed purchaser or other
     transferee ("Proposed Transferee"); (C) the quantity of Shares to be
     transferred to each Proposed Transferee; and (D) the terms and conditions
     of each proposed sale or transfer, including the price. Any such sale or
     other transfer shall be consummated within 30 days after the date of the
     Transfer Notice. Any such sale or other transfer shall be effected in
     accordance with any applicable securities laws and the Proposed Transferee
     shall agree in writing that the provisions of this Section 4(e) and the
     remaining restrictions and conditions contained in this Agreement shall
     continue to apply to the Shares in the hands of such Proposed Transferee.
     If the Shares described in the Transfer Notice are not transferred to the
     Proposed Transferee within such period, a new Transfer Notice shall be
     given to the Company before any Shares held by the Investor may be sold or
     otherwise transferred.

                                  Page 9 of 15
<PAGE>

      (f)  Transactions with Affiliates. The Company agrees that to the extent
           ----------------------------
it engages in transactions with Affiliates, it will do so upon fair and
reasonable terms, as if the transaction were with an unaffiliated party.


V.   TRANSFER AGENT INSTRUCTIONS. The Company shall issue irrevocable
instructions to its transfer agent to issue certificates, registered in the name
of the relevant Investor, for the Shares purchased by such Investor (the
"Irrevocable Transfer Agent Instructions"). Subsequent to the registration of
the Underlying Shares under the 1933 Act and Section 2 of the Registration
Rights Agreement, no such certificates shall bear the restrictive legend
specified in Section 2(i) of this Agreement. The Company warrants that no
instruction other than the Irrevocable Transfer Agent Instructions referred to
in this Section 5, and stop transfer instructions to give effect to Section 2(h)
hereof will be given by the Company to its transfer agent and that the Shares
shall otherwise be freely transferable on the books and records of the Company.
Nothing in this Section shall affect in any way the Investor's obligations and
agreement set forth in Section 2(i) hereof to comply with all applicable
prospectus delivery requirements, if any, upon resale of the Shares.


VI.  CONDITIONS TO THE COMPANY'S OBLIGATIONS. The obligation of the Company
hereunder to issue and sell the Common Stock to the Investor at the Closing is
subject to the satisfaction, at or before the Closing Date, respectively, of
each of the following conditions thereto, provided that these conditions are for
the Company's sole benefit and may be waived by the Company at any time in its
sole discretion:

     (a)   Representations and Warranties Correct. The representations and
           --------------------------------------
warranties made by the Investor in this Agreement hereof shall be true and
correct in all material respects on and as of the Closing Date with the same
effect as though such representations and warranties had first been made on and
as of the Execution Date and such Closing Date, respectively except for those
representations and warranties that address matters only as of a particular date
(which shall remain true and correct as of such particular date), with the same
effect as though such representations and warranties had first been made on and
as of the applicable Closing Date.

     (b)   Performance. All covenants, agreements and conditions contained in
           -----------
this Agreement to be performed by the Investor on or prior to the applicable
Closing Date shall have been performed or complied with in all material
respects.

     (c)   Execution of Documents. The Investor shall have executed this
           ----------------------
Agreement and the Registration Rights Agreement and delivered the same to the
Company. As of the Closing Date, each such agreement shall remain in full force
and effect.

     (d)   No Order Pending. There shall not then be in effect any order
           ----------------
enjoining or restraining the transactions contemplated by this Agreement.

     (e)   No Law Prohibiting or Restricting Such Sale. There shall not be in
           -------------------------------------------
effect any law, rule or regulation prohibiting or restricting such sale, or
requiring any consent or approval of

                                 Page 10 of 15
<PAGE>

any person which shall not have been obtained to issue the Shares (except as
otherwise provided in this Agreement).


VII. CONDITIONS TO INVESTOR'S OBLIGATIONS. The obligation of each Investor
hereunder (i) to execute this Agreement and (ii) to purchase the Shares is
subject to the satisfaction, at or before the Closing Date, of each of the
following conditions, provided that these conditions are such Investor's sole
benefit and may be waived by Investor at any time in its sole discretion:

     (a)   Representations and Warranties Correct. The representations and
           --------------------------------------
warranties made by the Company in Section 4 shall be true and correct in all
material respects on and as of the Execution Date or the Closing Date,
respectively, except for changes contemplated by this Agreement and except for
those representations and warranties that address matters only as of a
particular date (which shall remain true and correct as of such particular
date), with the same effect as through such representations and warranties had
been made on and as of the Execution Date or the Closing Date, respectively,
except in all cases where the failure of such representations and warranties to
be so true and correct would not (with respect to representations and warranties
not qualified by an Adverse Effect clause), individually or in the aggregate,
reasonably be expected to have an Adverse Effect on the Company and its
subsidiaries, taken as a whole.

     (b)   Performance. All covenants, agreements and conditions contained in
           -----------
the Transaction Documents to be performed by the Company on or prior to the
Closing Date shall have been performed or complied with in all material
respects.

     (c)   Execution of Documents. The Company shall have executed this
           ----------------------
Agreement, the Registration Rights Agreement and delivered the same to the
Investor. As of the Closing Date each such agreement shall remain in full force
and effect.

     (d)   No Order Pending. There shall not then be in effect any order
           ----------------
enjoining or restraining the transactions contemplated by this Agreement.

     (e)   No Law Prohibiting or Restricting Sale. There shall not be in
           --------------------------------------
effect any law, rule or regulation prohibiting or restricting such sale, or
requiring any consent or approval of any person which shall not have been
obtained to issue the Shares (except as otherwise referenced in this Agreement).

     (f)   Legal Opinion. The Investor shall have received an opinion of the
           -------------
Company's counsel, dated as of the Closing Date, in substantially the form as
Exhibit E attached hereto.

     (g)   Compliance Certificate. The Company shall have delivered to each
           ----------------------
Investor on the Closing Date a certificate executed by a duly authorized
officer, dated the applicable Closing Date, and certifying to the fulfillment of
the conditions specified in Sections 7(a) and 7(b).

     (h)   Insolvency. The Company is not insolvent and no Insolvency Proceeding
           ----------
has been commenced by or against the Company. As used herein, "Insolvency
Proceeding" means

                                 Page 11 of 15
<PAGE>

any proceeding commenced by or against any person or entity under any provision
of the United States Bankruptcy Code, as amended, or under any other bankruptcy
or insolvency law, including assignments for the benefit of creditors, formal or
informal moratoria, compositions, extension generally with its creditors, or
proceedings seeking reorganization, arrangement, or other relief.

     (i)   Reporting Status. The Company shall have filed all reports required
           ----------------
to be filed with the SEC pursuant to the Exchange Act, and the Company's status
as an issuer required to file reports under the Exchange Act shall be effective.


VIII. GOVERNING LAW; MISCELLANEOUS.

      (a)  Governing Law. This Agreement and all acts and transactions pursuant
           -------------
hereto and the rights and obligations of the parties hereto shall be governed,
construed and interpreted in accordance with the laws of the State of New York,
without giving effect to principles of conflicts of law. The parties hereby
irrevocably submit to the non-exclusive jurisdiction of the state and federal
courts sitting in the City of New York, borough of Manhattan, for the
adjudication of any dispute hereunder or in connection herewith or with any
transaction contemplated hereby or discussed herein (including with respect to
the enforcement of the any of the Transaction Documents), and hereby irrevocably
waives, and agrees not to assert in any suit, action or proceeding, any claim
that it is not personally subject to the jurisdiction of any such court, that
such suit, action or proceeding is improper.

      (b)  Counterparts; Signatures by Facsimile. This Agreement may be executed
           -------------------------------------
in counterparts and each such counterpart shall be deemed an original for all
purposes. In the event that any signature is delivered by facsimile
transmission, such signature shall create a valid and binding obligation of the
party executing (or on whose behalf such signature is executed) the same with
the same force and effect as if such facsimile signature page were an original
thereof.

      (c)  Captions and Headings. The captions and headings of this Agreement
           ---------------------
are for convenience and ease of reference only and are not intended to be a part
of or to affect the meaning or interpretation of this Agreement.

      (d)  Severability. If any term, provision, covenant or restriction of
           ------------
this Agreement is held by a court of competent jurisdiction to be invalid, void
or unenforceable, the remainder of the terms, provisions, covenants and
restrictions of this Agreement shall remain in full force and effect and shall
in no way be affected, impaired or invalidated.

      (e)  Entire Agreement; Amendment. This Agreement, the Registration
           ---------------------------
Rights Agreement and the other documents delivered pursuant hereto constitute
the full and entire understanding and agreement between the parties with regard
to the subject matter hereof and thereof and supersede all prior agreements and
understandings among the parties relating to the subject matter hereof. Neither
this Agreement nor any term hereof may be amended, waived, discharged or
terminated other than by a written instrument signed by the party against which
enforcement of any such amendment, waiver, discharge or termination is sought.

                                 Page 12 of 15
<PAGE>

      (f)  No Third Party Rights. Nothing in this Agreement shall create or be
           ---------------------
deemed to create any rights in any person or entity not a party to this
Agreement.

      (g)  Survival. Unless otherwise set forth in this Agreement, the
           --------
warranties, representations and covenants of the Company and the Investor
contained in or made pursuant to this Agreement shall survive the execution and
delivery of this Agreement and the Closing.

      (h)  Publicity. Each Investor and the Company shall not issue any public
           ---------
statement concerning the transactions contemplated by this Agreement without the
prior written consent of the parties named in such public statement not to be
unreasonably withheld; provided, however, that the parties may disclose the
transaction or the terms hereof or thereof from time to time without the
approval of the party whose name is disclosed if (i) such approval has been
requested and not received and such party concludes (after consulting with
counsel) that it is required by law to disclose the transaction or the terms
thereof or (ii) to the extent that similar disclosure has been previously
approved pursuant to this Section 8(h). In addition, with respect to any press
releases issued by the Company, the Company shall provide copies to the
Investors prior to public dissemination thereof and shall consider Investors'
comments to such press release, if any, in good faith.

      (i)  No Strict Construction. The language used in this Agreement will be
           ----------------------
deemed to be the language chosen by the parties o express their mutual intent,
and no rules of strict construction will be applied against any party.

      (j)  Costs and Expenses. Each party hereto shall pay its own costs and
           ------------------
expenses incurred in connection herewith, including the fees of its counsel,
auditors and other representatives, whether or not the transactions contemplated
herein are consummated.

      (k)  Brokers. The Company has not engaged, consented to or authorized any
           -------
broker, finder or intermediary to act on its behalf, directly or indirectly, as
a broker, finder or intermediary in connection with the transactions
contemplated by this Agreement, except for Paramount Capital, Inc. The Company
hereby agrees to indemnify and hold harmless each Investor and its respective
Affiliates from and against all fees, commissions or other payments owing to any
party acting on behalf of the Company hereunder.

      (l)  Notices. Any notices required or permitted to be given under the
           -------
terms of this Agreement shall be sent by certified or registered mail (return
receipt requested) or delivered personally or by courier (including a recognized
overnight delivery service) or by facsimile and shall be effective five days
after being placed in the mail, if mailed by regular U.S. mail, or upon receipt,
if delivered personally or by courier (including a recognized overnight delivery
service) or by facsimile, in each case addressed to a party. The addresses for
such communications shall be:

           If to the Company:

           Cell Therapeutics, Inc.
           201 Elliott Avenue West, Suite 400
           Seattle, Washington 9811

                                 Page 13 of 15
<PAGE>

           Attention: James Bianco, Chief Executive Officer
           Facsimile: (206) 284-6114

           With copy to:
           Wilson Sonsini Goodrich & Rosati
           975 Page Mill Road
           Palo Alto, California  94304
           Facsimile: (650) 461-5375
           Attention: Michael J. Kennedy, Esq.

           If to Investor at its address set forth on its signature page.

      Each party shall provide notice to the other party of any change in
address.

      (m)  Successors and Assigns. This Agreement shall be binding upon and
           ----------------------
inure to the benefit of the parties and their successors and permitted assigns.
Neither the Company nor any Investor may assign this Agreement or any rights or
obligations hereunder without the prior written consent of the other. This
Agreement shall be binding upon and shall inure to the benefit of the parties
hereto and their respective successors and permitted assigns.

      (n)  Remedies. In addition to being entitled to exercise all rights
           --------
provided herein or granted by law, including recovery of damages, each Investor
will be entitled to specific performance of the obligations of the Company under
the Transaction Documents. The Company and each Investor agree that monetary
damages may not be adequate compensation for any loss incurred by reason of any
breach of its obligations described in the foregoing sentence and hereby agrees
to waive in any action for specific performance of any such obligation the
defense that a remedy at law would be adequate.



                 [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

                                 Page 14 of 15
<PAGE>

         IN WITNESS WHEREOF, the undersigned Investor and the Company have
caused this Agreement to be duly executed as of the date first above written.


CELL THERAPEUTICS, INC.                    INVESTOR:____________________________


By:______________________________          By:__________________________________
   Name: James Bianco                      Name:________________________________
   Title: Chief Executive Officer          Title:_______________________________
                                           Address:_____________________________
                                                   _____________________________
                                                   _____________________________
                                           Tel:_________________________________
                                           Fax:_________________________________
                                           Soc. Sec./
                                           or Tax I.D.__________________________

                                 Page 15 of 15