<PAGE>
                                                                    Exhibit 4.24

                                RIGHTS AGREEMENT

     This Rights Agreement (this "Agreement"), effective July 27, 2005, is made
between Icahn Partners LP, Icahn Partners Master Fund LP, High River Limited
Partnership (collectively, the "Icahn Purchasers"), Viking Global Equities LP
and VGE III Portfolio Ltd. (collectively, "Viking," and collectively with the
Icahn Purchasers, the "Purchasers") and ADVENTRX Pharmaceuticals, Inc., a
Delaware corporation (the "Company"). Capitalized terms used but not otherwise
defined in this Agreement have the meaning ascribed to them in the Securities
Purchase Agreement, dated July 21, 2005 (the "Purchase Agreement"), by and among
the Company, the Purchasers and the other entities listed on Appendix A thereto.

                                   BACKGROUND

     A. Pursuant to the Purchase Agreement, at the Closing the Purchasers would
purchase and the Company would issue to the Purchasers an aggregate
approximately $14,000,000 of Shares and, for no additional consideration,
Warrants to purchase a number of shares of Common Stock in the aggregate equal
to 100% of the number of Shares purchased at a price of $2.26 (the "Purchaser
Warrants").

     B. The Company is entering into this Agreement to induce the Purchasers to
enter into and perform the Purchase Agreement.

                                    AGREEMENT

     In consideration of the mutual covenants and agreements set forth herein
and for good and valuable consideration, the receipt and adequacy of which are
hereby acknowledged, the parties agree as follows:

1. CONSENT RIGHT.

     1.1 ADDITIONAL SHARES. The Company hereby agrees that it shall not at any
time after the date of the Closing and prior to July 27, 2006, without the prior
written consent of Purchasers which at the time own a majority of the Purchased
Shares (as that term is defined below), issue any shares of its Common Stock
other than Consent Excluded Shares in exchange for consideration, determined in
accordance with the following sentences, in an amount per share less than the
Exercise Price (as such term is defined in the Purchaser Warrants.) (For
purposes of this Agreement, the term "issue" includes any issue or sale of
Common Stock by the Company, whether of newly-issued shares or treasury shares,
and the term "Purchased Shares" means on any date the sum of the number of
Shares, plus the number of Warrant Shares for which the Purchaser Warrants have
been exercised, that are owned in the aggregate by the Purchasers.) In the case
of the issuance of shares of Common Stock for cash, the consideration received
by the Company shall be deemed to be the amount of cash paid therefor after
deducting any discounts, commissions or other expenses of underwriters, sales
agents or brokers allowed, paid or incurred by the Company for any underwriting
or otherwise in connection with the issuance thereof. In the case of the
issuance of shares of Common Stock for a consideration in whole or in part other
than cash, the consideration other than cash shall be valued at the fair value
thereof.
<PAGE>
     1.2 COMMON STOCK EQUIVALENTS. The Company hereby agrees that it shall not
at any time after the date of the Closing and prior to July 27, 2006, without
the prior written consent of the Purchasers which at the time own a majority of
the Purchased Shares, issue or sell any warrants, options or other rights to
subscribe for or purchase any additional shares of Common Stock or any
securities convertible into or exchangeable for shares of Common Stock (other
than Consent Excluded Shares) (collectively, "Common Stock Equivalents"),
whether or not the rights to exchange or convert thereunder are immediately
exercisable, and the effective price per share for which Common Stock is
issuable upon the exercise, exchange or conversion of such Common Stock
Equivalents shall be less than the Exercise Price.

     1.3 CONSENT EXCLUDED SHARES. For purposes of this Agreement the term
"Consent Excluded Shares" means: (i) up to 1,000,000 shares of Common Stock or
Common Stock Equivalents issued or issuable after the date of Closing to
officers, employees, directors or consultants of the Company, as approved by the
Board under incentive plans and in addition no officer, employee, director or
consultant can receive Common Stock or Common Stock Equivalents for more than an
aggregate of 100,000 shares of Common Stock; (ii) shares of Common Stock
issuable upon exercise of warrants, options or other rights to acquire
securities of the Company, in each case, outstanding on the date of the Closing;
(iii) the Shares; (iv) the Warrants and the Warrant Shares; (v) up to 200,000
shares of Common Stock issued or issuable to existing licensors of technology of
the Company to pay expenses, royalties or milestone payments for which the
Company is or becomes obligated under any licensing or related agreement; (vi)
up to 150,000 shares of Common Stock or Common Stock Equivalents issued or
issuable after the Closing Date for non-equity financing purposes, and as
approved by the Board, to financial institutions or lessors in connection with
commercial credit arrangements, equipment financings or similar transactions;
(vii) shares of Common Stock issuable or issued pursuant to stock splits and
stock dividends; and (viii) shares of Common Stock issued or issuable by way of
dividend or other distribution on outstanding shares.

     1.4 TERMINATION OF CONSENT RIGHTS. The consent rights of the Purchasers
contained in this Section 1 shall automatically terminate and be of no further
force and effect upon the earlier of (i) July 27, 2006; (ii) the date that the
Purchasers' aggregate holdings of Purchased Shares (either of record or
beneficially) is as a result of sales or other dispositions thereof equal to
less than 50% of the aggregate number of Shares purchased by the Purchasers
pursuant to the Purchase Agreement; and (iii) at the time of a Change of
Control. For purposes of this Section 1.4 and without limitation, the holdings
of the Purchasers will be determined on a net basis after giving effect to any
sale or other disposition, contract or option to sell any shares of Common
Stock, and any swap or other arrangement that transfers to another, in whole or
in part, any of the economic consequences of ownership of shares of Common
Stock, whether such arrangement provides for settlement by delivery of
securities, the payment of cash or otherwise. For purposes of this Agreement,
the term "Change of Control" means (A) any acquisition of the Company (whether
or not the Company is the surviving corporation) by means of merger,
consolidation or other form of corporate reorganization (other than a
reincorporation transaction or change of domicile) following which the holders
of the outstanding voting securities of the Company immediately prior to such
merger, consolidation or other reorganization do not hold (in their capacity as
such) equity securities representing a majority of the voting power of the
surviving or resulting entity immediately following such merger, consolidation
or other reorganization or (B) a sale of all or substantially all of the assets
of the Company other than to a buyer in which


                                       2
<PAGE>
the holders of the outstanding voting securities of the Company immediately
prior to such sale hold (in their capacity as such) equity securities
representing a majority of the voting power immediately following such sale.

     1.5 ADDITIONAL RESTRICTIONS. During the period specified in Section 1.4,
the Company agrees that (i) except for the Consent Excluded Shares, it will not
issue any shares of Common Stock or Common Stock Equivalents to any executive
officer of the Company, and (ii) no Common Stock or Common Stock Equivalents
shall be issued to Mr. Evan Levine.

2. PARTICIPATION RIGHTS.

     2.1 RIGHT AND NOTICE. Subject to the terms and conditions specified in this
Section 2, the Company grants to the Purchasers a right to participate in future
sales by the Company of any Additional Securities (as hereinafter defined), and
the Company shall not issue any Additional Securities unless the Company
complies with the provisions of this Section 2. The term "Additional Securities"
means any shares of, or securities convertible into or exercisable for any
shares of, any class of its capital stock or any other securities. Each time the
Company proposes to make an offer of any Additional Securities, the Company
shall deliver a written notice ("Notice") to the Purchasers stating (i) its bona
fide intention to offer such Additional Securities, (ii) the anticipated number
of such Additional Securities to be offered, and (iii) the anticipated price and
terms, if any, upon which it proposes to offer such Additional Securities. The
Company will not issue any Additional Securities for non-cash consideration
unless prior thereto the Company and the Purchasers which at the time own a
majority of the Purchased Shares agree on the value thereof and the Purchasers
can exercise their rights under this Section 2 by the payment of cash. The
participation rights of the Purchasers under this Section 2 shall, in the
absence of agreement among themselves, be on a pro rata basis with respect to
the number of Purchased Shares at the time owned by each Purchaser; and
provided, however, that if any Purchaser does not participate in its full pro
rata share of Additional Securities, then the other Purchasers can participate
in the sale of such remaining Additional Securities on the same pro rata basis
until such Purchasers participate in the entire amount of such Additional
Securities or such lesser amount in which they decide to participate.

     2.2 PUBLIC OFFERING. In any issuance of Additional Securities that is being
registered for sale to the public, the Purchasers shall have the right to
purchase, in the aggregate, up to (i) 50% of the Additional Securities decided
by the Company to be sold in such public offering if the offering price of the
stock is equal to or below $8.00 per share, and (ii) 20% of the Additional
Securities decided by the Company to be sold in such public offering if the
offering price of the stock is above $8.00 per share, in each case on the same
terms and conditions (including the same price, but after subtracting any
underwriting discount or commission) as the other initial public purchasers in
such offering. The Company shall have the right to disclose in any prospectus
the name of the Purchasers participating therein and the amount Additional
Securities to be purchased by them. For purposes of calculating the amount of
Additional Securities the Purchasers may purchase under this Section 2, it will
be assumed that the underwriters have fully exercised (or will fully exercise)
any over-allotment option.

     2.3 PRIVATE OFFERING. In any issuance of Additional Securities that is not
being registered for sale to the public (which shall include a PIPE financing),
the Purchasers shall have


                                        3
<PAGE>
the right to purchase, in the aggregate, up to 50% of the amount of Additional
Securities finally agreed by the Company to be sold in such private offering to
all parties (including the Purchasers) on the same terms and conditions
(including the same price and registration rights) as the other purchasers in
such offering. In addition to the other provisions of this Section 2.3, the
Purchasers desiring to exercise their rights under this Section 2.3 must make
the same representations and warranties as the other purchasers under this
Section 2.3 to establish an exemption from registration under the Securities
Act.

     2.4 NOTICE AND INTENTION TO PURCHASE. The Company shall deliver the Notice
to the Purchasers at least 15 days but not later than 30 days prior to the sale
of the Additional Securities, and each Purchaser shall give the Company notice
that it may participate in purchasing, up to that portion of such Additional
Securities to which it is entitled hereunder by giving notice to the Company of
its intention to do the same within 10 days after its receipt of the Notice.
Thereafter, in connection with any offering under Section 2.2 or Section 2.3 for
which a notice to participate is given under Section 2.4, the Purchasers must
agree and affirm to the Company on the day of pricing of the Additional
Securities (but immediately following the actual pricing of the Additional
Securities) that it or they are committed to purchase the amount of the
Additional Securities selected by them, at the final price and terms for the
offering, in which event it or they will have the right and obligation to
participate in such offering.

     2.5 NON-ELECTION. If the Purchasers elect not to purchase any Additional
Securities or do not give notice of participation in accordance with this
Section 2, the Company may, during the 45-day period following the expiration of
the period provided in Section 2.4, offer the Additional Securities to any
person or persons at a price not less than, of a quantity not more than and upon
terms no more favorable to the offeree than those specified in the Notice.
Thereafter, the right provided hereunder shall be deemed to be revived and
Additional Securities shall not be offered unless first offered to the
Purchasers in accordance herewith.

     2.6 PARTICIPATION EXCLUDED SHARES. The rights granted in this Section 2
shall not be applicable to the issuance or sale of any Participation Excluded
Shares. For purposes of this Agreement the term "Participation Excluded Shares"
means: (i) the Consent Excluded Shares covered by sections (ii), (iii), (iv),
(vii) and (viii) of Section 1.3 hereof; (ii) up to 4,500,000 shares in the
aggregate of Common Stock or Common Stock Equivalents issued or issuable after
the date of Closing to officers, employees, directors or consultants of the
Company, as approved by the Board under incentive plans; (iii) up to 1,500,000
shares in the aggregate of Common Stock issued or issuable to existing licensors
of technology of the Company to pay expenses, royalties or milestone payments
for which the Company is or becomes obligated under any licensing or related
agreement; and (iv) up to 1,000,000 shares in the aggregate of Common Stock or
Common Stock Equivalents issued or issuable after the Closing Date for
non-equity financing purposes, and as approved by the Board, to financial
institutions or lessors in connection with commercial credit arrangements,
equipment financings or similar transactions. Furthermore, with respect to the
Common Stock and Common Stock Equivalents covered by sections (ii), (iii) and
(iv) of the preceding sentence, no more than 20% of the amount of such Common
Stock or Common Stock Equivalents may be issued in any twelve-month period
commencing on the date hereof.


                                       4
<PAGE>
     2.7 TERMINATION OF PARTICIPATION RIGHTS. The participation rights of the
Purchasers contained in this Section 2 shall automatically terminate and be of
no further force and effect upon the earlier of (i) July 27, 2012; (ii) the date
that the Purchasers' aggregate holdings of Purchased Shares (either of record or
beneficially) is as a result of sales or other dispositions thereof equal to
less than 50% of the aggregate number of Shares purchased by the Purchasers
pursuant to the Purchase Agreement; and (iii) at the time of a Change of
Control. For purposes of this Section 2.7 and without limitation, the holdings
of the Purchasers will be determined on a net basis after giving effect to any
sale or other disposition, contract or option to sell any shares of Common
Stock, and any swap or other arrangement that transfers to another, in whole or
in part, any of the economic consequences of ownership of shares of Common
Stock, whether such arrangement provides for settlement by delivery of
securities, the payment of cash or otherwise.

3. CHANGE OF CONTROL PROVISIONS. At any time that the Company makes, receives or
considers any proposal for a transaction which, if consummated, would constitute
a Change of Control and the Board of Directors has decided to approve such
transaction and, if required, recommend the stockholders vote to approve such
transaction, then the Company agrees that (a) no binding or definitive agreement
with respect thereto shall contain any break-up fee provisions or similar types
of provisions, except that the Company may agree to reimburse reasonable
out-of-pocket due diligence expenses, and (b) it shall not consummate such
Change of Control unless the Company shall call a stockholders' meeting or
conduct a consent solicitation for approval by the stockholders of the Change of
Control, in which meeting or solicitation the approval of the holders of the
number of shares required by the Delaware General Corporation Law and/or any
stock exchange to approve the Change of Control is obtained or, if no such
approval is required, the approval of the holders of a majority of the
outstanding shares of stock entitled to vote in attendance at a meeting at which
a quorum is present is obtained.

4. BOARD OF DIRECTORS. Effective promptly after the Closing, the Company shall
set the authorized number of Board directors at six and the Company shall
appoint a person suggested by the Purchasers which at the time own a majority of
the Purchased Shares to the vacancy so created; provided that such person, if
anyone other than Mr. Carl Icahn, would not subject the Company to making any
disclosures under Item 401(f) of SEC Regulation S-K in any proxy statement (the
"Criteria"). Prior to any appointment of such person, he or she will provide all
of the information required by the Form 8-K which will need to be filed with
respect thereto. Thereafter, as long as the Purchasers have any participation
rights under Section 2 hereof, the Company shall cause the Board of Directors to
nominate a Board nominee selected by the Purchasers in the manner set forth
above as long as such person, if anyone other than Mr. Carl Icahn, satisfies the
Criteria.

5. RIGHTS PLAN AND CLASSIFIED BOARD.

     5.1 RIGHTS PLAN. The Company agrees that as long as the Purchasers have any
participation rights under Section 2 hereof, it shall not adopt any rights plan.
For purposes of this Agreement, a "rights plan" shall include any plan,
agreement or other device adopted by the Board of Directors designed to prevent
a hostile takeover by increasing the takeover cost either through the issuance
of new rights, common or preferred shares or any other security or device that
are issued to shareholders of the Company other than all shareholders of the
Company that carry severe redemption provisions, favorable purchase provisions
or otherwise.


                                       5
<PAGE>
     5.2 CLASSIFIED BOARD. The Company hereby agrees that as long as the
Purchasers have any participation rights under Section 2 hereof, it shall not
adopt a classified Board, nor change the authorized number of Board directors as
set forth in Section 4.

     5.3 CHARTER AMENDMENTS. In furtherance of Sections 5.1 and 5.2, the Company
agrees that it shall hold a meeting of its stockholders, or conduct a written
consent solicitation of stockholders, to propose amendments to its charter
documents to expressly prohibit the adoption of a rights plan and the adoption
of a classified board (the "Proposals"). The Company agrees that the Board of
Directors shall recommend the Proposals and the Company shall use its best
efforts to procure stockholder approval of the Proposals. The Company shall hold
said stockholders' meeting, or complete the written consent solicitation, no
later than November 15, 2005, and shall set the record date for such meeting or
solicitation after the date of the Closing. However, if for any reason the Board
of Directors of the Company breaches this Agreement by adopting a rights plan or
implementing a classified Board of Directors, then within 30 days thereafter any
or all of the Purchasers can elect to rescind its purchase of any of (i) the
Shares purchased by it and Warrant Shares exercised by it which in each case
have not been sold or otherwise disposed of, and (ii) the Warrants. The
rescission price for any such Shares and Warrant Shares shall equal the greater
of $2.50 or the average of the closing prices of the Common Stock for the 10
business days before any such notice is given (the "Average Price"). The
rescission price for any unexercised Warrant shall be the number of shares for
which the Warrant has not been exercised multiplied by the difference between
the Average Price minus the $1.85. The Company shall also reimburse the
Purchasers for its costs in the negotiation of the Purchase Agreement, the
Purchaser Warrants and this Agreement.

     5.4 VOTING. At the Closing, the Company shall present the Purchasers with
the written binding agreement of the beneficial owners of not less than an
aggregate of 9,000,000 shares of Common Stock to vote such shares owned by them
at the time of the meeting or solicitation for the adoption of such amendments.
The Purchasers agree to vote all shares of Common Stock owned by them at the
time of such meeting or solicitation in favor of such amendments.

6. MISCELLANEOUS.

     6.1 NOTICES.

          (A) All notices, requests, consents and other communications hereunder
shall be in writing, shall be mailed by first-class registered or certified
airmail, confirmed facsimile or nationally recognized overnight express courier
postage prepaid, and shall be as addressed as follows:


                                       6
<PAGE>
                    if to the Company, to:

                       ADVENTRX Pharmaceuticals, Inc.
                       6725 Mesa Ridge Road, Suite 100
                       San Diego, California 92121
                       Attention: Chief Executive Officer
                       Telephone No.: (858) 552-0866
                       Telecopy No.: (858) 552-0876

                    with a copy to (not to constitute notice):

                       Bingham McCutchen LLP
                       Three Embarcadero Center
                       San Francisco, CA 94111
                       Attention: Hank Evans
                                  Francis Sarena
                       Telephone No.: (415) 393-2000
                       Telecopy No.: (415) 393-2286

                    if to any Icahn Purchaser, to such Purchaser at:

                       767 Fifth Avenue
                       47th Floor
                       New York, NY 10153
                       Attention: Marc Weitzen, Esq.
                       Telephone No.: (212) 702-4300
                       Telecopy No.: (212) 750-5815

                    if to Viking:

                       55 Railroad Avenue
                       Greenwich, CT 06830
                       Attention: Alex Denner
                       Telephone No.: (203) 863-5000
                       Telecopy No.: (203) 625-8705

or at such other address or addresses as may have been previously furnished to
the other party in writing in accordance with this Section 6.1.

          (B) Such notices or other communications shall be deemed delivered
upon receipt, in the case of overnight delivery, personal delivery, facsimile
transmission (as evidenced by the confirmation thereof), or mail.

     6.2 AMENDMENTS. Any term of this Agreement may be amended and the
observance of any term of this Agreement may be waived (either generally or in a
particular instance and either retroactively or prospectively) only with the
written consent of the Company and Icahn.


                                       7
<PAGE>
     6.3 HEADINGS. The headings of the various sections of this Agreement are
for convenience of reference only and shall not be deemed to be part of this
Agreement.

     6.4 SEVERABILITY. In the event that any provision in this Agreement is held
to be invalid, illegal or unenforceable in any respect, the validity, legality
and enforceability of the remaining provisions contained herein shall not in any
way be affected or impaired thereby.

     6.5 INJUNCTIVE RELIEF. Notwithstanding any other provisions of this
Agreement, a breach of any of the provisions of this Agreement by the Company
will cause the Purchasers irreparable damage for which recovery of money damages
shall be inadequate, and the Purchasers shall therefore be entitled to obtain
injunctive relief (without any requirement to post any bond) and specific
performance to protect their rights and enforce the terms and provisions under
this Agreement in addition to any and all remedies available to them at law or
in equity.

     6.6 GOVERNING LAW AND FORUM. This Agreement shall be governed by and
construed in accordance with the laws of the State of New York applicable to
agreements made and to be fully performed therein. The parties hereto agree to
submit to the exclusive jurisdiction of the federal and state courts of the
State of New York with respect to the interpretation of this Agreement or for
the purposes of any action arising out of or related to this Agreement.

     6.7 COUNTERPARTS. This Agreement may be executed in counterparts, each of
which shall constitute an original, and all of which together shall constitute
one and the same instrument. In the event that any signature is delivered via
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 hereof.

     6.8 ENTIRE AGREEMENT. This Agreement contains the entire understanding of
the parties with respect to the matters covered herein, supersedes all prior
agreements and understandings with respect to such matters and executed by and
between the Company and Icahn.

     6.9 EXPENSES. Each party shall pay all costs and expenses incurred by it in
connection with the execution and delivery of this Agreement, and all the
transactions contemplated thereby, including fees of legal counsel.

        [Remainder of page intentionally blank; signature page follows.]


                                       8
<PAGE>
     IN WITNESS WHEREOF, the parties hereto have caused this Rights Agreement to
be executed as of the date first written above.

                                        ADVENTRX PHARMACEUTICALS, INC.


                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------


                                        ICAHN PARTNERS LP


                                        By:
                                            ------------------------------------
                                        Name: Keith Meister
                                        Title: Authorized Signatory


                                        ICAHN PARTNERS MASTER FUND LP


                                        By:
                                            ------------------------------------
                                        Name: Keith Meister
                                        Title: Authorized Signatory


                                        HIGH RIVER LIMITED PARTNERSHIP

                                        By: Hopper Investments, LLC, its general
                                            partner

                                        By: Barberry Corp., its sole member


                                        By:
                                            ------------------------------------
                                        Name: Edward E. Mattner
                                        Title: Authorized Signatory


                                        VIKING GLOBAL EQUITIES LP


                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------


                                        VGE III PORTFOLIO LTD.


                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------


                       SIGNATURE PAGE TO RIGHTS AGREEMENT