SC 13G


VIKING GLOBAL PERFORMANCE LLC
VIKING GLOBAL INVESTORS LP
VIKING GLOBAL EQUITIES LP
O. ANDREAS HALVORSEN
BRIAN T. OLSON
DAVID C. OTT
NASD

0001160308
Adventrx Pharmaceuticals, Inc.
84-1318182


CARL CASLER
203-863-5039

0001132625
c4tercp$

SC 13G

viking1.txt




                 SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                                ________________

                              Schedule 13G
                                 (Rule 13d-102)
                                ________________

INFORMATION TO BE INCLUDED IN STATEMENTS PURSUANT TO RULES 13d-1(b),(c)
              AND (d) AND AMENDMENTS THERETO FILED PURSUANT TO 13d-2
                 UNDER THE SECURITIES EXCHANGE ACT OF 1934*

                            Adventrx Pharmaceuticals, Inc.
                                 (Name of Issuer)

                                    Common Stock
                         (Title of Class of Securities)

                                     00764X103
                                  (CUSIP Number)

                    July 26, 2005, based on the Securities Purchase Agreement
                                      entered into on July 26, 2005
                      (Date of Event Which Requires Filing of this Statement)


     Check the appropriate box to designate the rule pursuant to which this
Schedule is filed:
     [ ]    Rule 13d-1(b)
     [X]  Rule 13d-1(c)
     [ ]    Rule 13d-1(d)

___________

     *  The remainder of this cover page shall be filled out for a reporting
person's initial filing on this form with respect to the subject class of
securities, and for any subsequent amendment containing information which
would alter the disclosures provided in a prior cover page.


     The information required in the remainder of this cover page shall not
be deemed to be "filed" for the purpose of Section 18 of the Securities
Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that
section of the Act but shall be subject to all other provisions of the Act
(however, see the Notes).



Schedule 13G PAGE 2 OF 12 CUSIP No. 00764X103 _____________________________________________________________________________ (1) NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Viking Global Performance LLC _____________________________________________________________________________ (2) CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) [ ] (b) [x] _____________________________________________________________________________ (3) SEC USE ONLY _____________________________________________________________________________ (4) CITIZENSHIP OR PLACE OF ORGANIZATION Delaware _____________________________________________________________________________ NUMBER OF (5) SOLE VOTING POWER 0 SHARES ______________________________________________________________ BENEFICIALLY (6) SHARED VOTING POWER 3,783,783 OWNED BY ______________________________________________________________ EACH (7) SOLE DISPOSITIVE POWER 0 REPORTING ______________________________________________________________ PERSON WITH (8) SHARED DISPOSITIVE POWER 3,783,783 _____________________________________________________________________________ (9) AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 3,783,783 _____________________________________________________________________________ (10) CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES [ ] _____________________________________________________________________________ (11) PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 5.7% _____________________________________________________________________________ (12) TYPE OF REPORTING PERSON OO _____________________________________________________________________________

Schedule 13G PAGE 3 OF 12 CUSIP No. 00764X103 _____________________________________________________________________________ (1) NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Viking Global Investors LP _____________________________________________________________________________ (2) CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) [ ] (b) [x] _____________________________________________________________________________ (3) SEC USE ONLY _____________________________________________________________________________ (4) CITIZENSHIP OR PLACE OF ORGANIZATION Delaware _____________________________________________________________________________ NUMBER OF (5) SOLE VOTING POWER 0 SHARES ______________________________________________________________ BENEFICIALLY (6) SHARED VOTING POWER 3,783,783 OWNED BY ______________________________________________________________ EACH (7) SOLE DISPOSITIVE POWER 0 REPORTING ______________________________________________________________ PERSON WITH (8) SHARED DISPOSITIVE POWER 3,783,783 _____________________________________________________________________________ (9) AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 3,783,783 _____________________________________________________________________________ (10) CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES [ ] _____________________________________________________________________________ (11) PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 5.7% _____________________________________________________________________________ (12) TYPE OF REPORTING PERSON PN _____________________________________________________________________________

Schedule 13G PAGE 4 OF 12 CUSIP No. 00764X103 _____________________________________________________________________________ (1) NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Viking Global Equities LP _____________________________________________________________________________ (2) CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) [ ] (b) [x] _____________________________________________________________________________ (3) SEC USE ONLY _____________________________________________________________________________ (4) CITIZENSHIP OR PLACE OF ORGANIZATION Delaware _____________________________________________________________________________ NUMBER OF (5) SOLE VOTING POWER 0 SHARES ______________________________________________________________ BENEFICIALLY (6) SHARED VOTING POWER 1,832,483 OWNED BY ______________________________________________________________ EACH (7) SOLE DISPOSITIVE POWER 0 REPORTING ______________________________________________________________ PERSON WITH (8) SHARED DISPOSITIVE POWER 1,832,483 _____________________________________________________________________________ (9) AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 1,832,483 _____________________________________________________________________________ (10) CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES [ ] _____________________________________________________________________________ (11) PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 2.8% _____________________________________________________________________________ (12) TYPE OF REPORTING PERSON PN _____________________________________________________________________________

Schedule 13G PAGE 5 OF 12 CUSIP No. 00764X103 _____________________________________________________________________________ (1) NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON O. Andreas Halvorsen _____________________________________________________________________________ (2) CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) [ ] (b) [x] _____________________________________________________________________________ (3) SEC USE ONLY _____________________________________________________________________________ (4) CITIZENSHIP OR PLACE OF ORGANIZATION Norway _____________________________________________________________________________ NUMBER OF (5) SOLE VOTING POWER 0 SHARES ______________________________________________________________ BENEFICIALLY (6) SHARED VOTING POWER 3,783,783 OWNED BY ______________________________________________________________ EACH (7) SOLE DISPOSITIVE POWER 0 REPORTING ______________________________________________________________ PERSON WITH (8) SHARED DISPOSITIVE POWER 3,783,783 _____________________________________________________________________________ (9) AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 3,783,783 _____________________________________________________________________________ (10) CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES [ ] _____________________________________________________________________________ (11) PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 5.7% _____________________________________________________________________________ (12) TYPE OF REPORTING PERSON IN _____________________________________________________________________________

Schedule 13G PAGE 6 OF 12 CUSIP No. 00764X103 _____________________________________________________________________________ (1) NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Brian T. Olson _____________________________________________________________________________ (2) CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) [ ] (b) [x] _____________________________________________________________________________ (3) SEC USE ONLY _____________________________________________________________________________ (4) CITIZENSHIP OR PLACE OF ORGANIZATION United States _____________________________________________________________________________ NUMBER OF (5) SOLE VOTING POWER 0 SHARES ______________________________________________________________ BENEFICIALLY (6) SHARED VOTING POWER 3,783,783 OWNED BY ______________________________________________________________ EACH (7) SOLE DISPOSITIVE POWER 0 REPORTING ______________________________________________________________ PERSON WITH (8) SHARED DISPOSITIVE POWER 3,783,783 _____________________________________________________________________________ (9) AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 3,783,783 _____________________________________________________________________________ (10) CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES [ ] _____________________________________________________________________________ (11) PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 5.7% _____________________________________________________________________________ (12) TYPE OF REPORTING PERSON IN _____________________________________________________________________________

Schedule 13G PAGE 7 OF 12 CUSIP No. 00764X103 _____________________________________________________________________________ (1) NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON David C. Ott _____________________________________________________________________________ (2) CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) [ ] (b) [x] _____________________________________________________________________________ (3) SEC USE ONLY _____________________________________________________________________________ (4) CITIZENSHIP OR PLACE OF ORGANIZATION United States _____________________________________________________________________________ NUMBER OF (5) SOLE VOTING POWER 0 SHARES ______________________________________________________________ BENEFICIALLY (6) SHARED VOTING POWER 3,783,783 OWNED BY ______________________________________________________________ EACH (7) SOLE DISPOSITIVE POWER 0 REPORTING ______________________________________________________________ PERSON WITH (8) SHARED DISPOSITIVE POWER 3,783,783 _____________________________________________________________________________ (9) AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 3,783,783 _____________________________________________________________________________ (10) CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES [ ] _____________________________________________________________________________ (11) PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 5.7% _____________________________________________________________________________ (12) TYPE OF REPORTING PERSON IN _____________________________________________________________________________

Schedule 13G PAGE 8 OF 12 ITEM 1(a). NAME OF ISSUER: Adventrx Pharmaceuticals, Inc. ITEM 1(b). ADDRESS OF ISSUER'S PRINCIPAL EXECUTIVE OFFICES: 6725 Mesa Ridge Road, Suite 100, San Diego, California 92121 ITEM 2(a). NAME OF PERSON FILING: Viking Global Performance LLC ("VGP"), Viking Global Investors LP ("VGI"), Viking Global Equities LP ("VGE"), O. Andreas Halvorsen, Brian T.Olson, and David C. Ott. ITEM 2(b). ADDRESS OF PRINCIPAL OFFICE OR, IF NONE, RESIDENCE: The business address of each of the Reporting Persons is 55 Railroad Avenue, Greenwich, CT 06830. ITEM 2(c). CITIZENSHIP: VGE and VGI are each Delaware limited partnerships and VGP is a Delaware limited liability company. O. Andreas Halvorsen is a citizen of Norway, and Brian T. Olson and David C. Ott are citizens of the United States. ITEM 2(d). TITLE OF CLASS OF SECURITIES: Common Stock ITEM 2(e). CUSIP NUMBER: 00764X103 ITEM 3. IF THIS STATEMENT IS FILED PURSUANT TO 13d-1(b) OR 13d-2(b) OR (c), CHECK WHETHER THE PERSON FILING IS A: (a) [ ] Broker or dealer registered under Section 15 of the Act (b) [ ] Bank as defined in Section 3(a)(6) of the Act (c) [ ] Insurance Company as defined in Section 3(a)(19) of the Act (d) [ ] Investment Company registered under Section 8 of the Investment Company Act of 1940 (e) [ ] Investment Adviser registered under Section 203 of the Investment Advisers Act of 1940: see Rule 13d- 1(b)(1)(ii)(E) (f) [ ] Employee Benefit Plan, Pension Fund which is subject to the provisions of the Employee Retirement Income Security Act of 1974 or Endowment Fund; see Rule 13d- 1(b)(1)(ii)(F)

Schedule 13G PAGE 9 OF 12 (g) [ ] Parent Holding Company, in accordance with Rule 13d- 1(b)(ii)(G); (h) [ ] Savings Associations as defined in Section 3(b) of the Federal Deposit Insurance Act; (i) [ ] Church Plan that is excluded from the definition of an investment company under Section 3(c)(14) of the Investment Company Act of 1940; (j) [ ] Group, in accordance with Rule 13d-1(b)(1)(ii)(J). IF THIS STATEMENT IS FILED PURSUANT TO Rule 13d-1(c), CHECK THIS BOX. [x] ITEM 4. OWNERSHIP. A. VGP and VGI (a) Amount beneficially owned 3,783,783 (b) Percent of class: 5.7% (All percentages herein are based on 65,933,730 shares of Common Stock reported to be outstanding as of July 21, 2005 as reflected in the Company's Form 8-K filed with the Securities and Exchange Commission by the Company on July 27, 2005) (c) Number of shares as to which such person has: (i) sole power to vote or to direct the vote 0 (ii) shared power to vote or to direct the vote 3,783,783 (iii) sole power to dispose or to direct the disposition of 0 (iv) shared power to dispose or to direct the disposition of 3,783,783 VGP, as the general partner of VGE and VGI,an affiliate of VGP,that provides managerial services to VGE, each have the power to dispose of and vote the shares of Common Stock directly owned by VGE. VGP and VGI are parties to an investment management agreement with VGE III Portfolio Ltd. which is a company organized under the laws of the Cayman Islands, pursuant to which VGP has investment authority with respect to securities held in such accounts and VGI performs managerial services in connection with such accounts. VGP and VGI have authority to dispose of and vote securities held in such accounts. Neither VGP nor VGI owns directly any shares of Common Stock.

Schedule 13G PAGE 10 OF 12 By reason of the provisions of Rule 13d-3 of the Securities Exchange Act of 1934 as amended (the "Act"), VGP and VGI may each be deemed to own beneficially shares directly held by VGE, and VGE III Portfolio Ltd. B. VGE (a) Amount beneficially owned: 1,832,483 (b) Percent of class: 2.8% (c) Number of shares as to which such person has: (i) sole power to vote or to direct the vote 0 (ii) shared power to vote or to direct the vote 1,832,483 (iii) sole power to dispose or to direct the disposition of 0 (iv) shared power to dispose or to direct the disposition of 1,832,483 VGE has the power to dispose of and the power to vote the shares of Common Stock directly owned by it, which power may be exercised by its general partner, VGP and by VGI, an affiliate of VGP, which provides managerial services to VGE. C. O. Andreas Halvorsen, Brian T. Olson, and David C. Ott (a) Amount beneficially owned: 3,783,783 (b) Percent of class: 5.7% (c) Number of shares as to which such person has: (i) sole power to vote or to direct the vote 0 (ii) shared power to vote or to direct the vote 3,783,783 (iii) sole power to dispose or to direct the disposition of 0 (iv) shared power to dispose or to direct the disposition of 3,783,783 Messrs. Halvorsen, Olson, and Ott, as Managing Directors of VGI and Members of VGP, have shared power to dispose of and shared power to vote the Common Stock beneficially owned by VGI and VGP. None of Messrs. Halvorsen, Olson, or Ott directly own any shares of Common Stock. By reason of the provisions of Rule 13d-3 of the Act, each may be deemed to beneficially own the shares directly owned by VGE and VGE III Portfolio Ltd.

Schedule 13G PAGE 11 OF 12 ITEM 5. OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS. If this statement is being filed to report the fact that as of the date hereof the Reporting Persons has ceased to be the beneficial owner of more than five percent of the class of securities, check the following.[] ITEM 6. OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON. See Item 4. ITEM 7. IDENTIFICATION AND CLASSIFICATION OF THE SUBSIDIARY WHICH ACQUIRED THE SECURITY BEING REPORTED ON BY THE PARENT HOLDING COMPANY. Not applicable. ITEM 8. IDENTIFICATION AND CLASSIFICATION OF MEMBERS OF THE GROUP. Not applicable. ITEM 9. NOTICE OF DISSOLUTION OF GROUP. Not applicable. ITEM 10. CERTIFICATION. (if filing pursuant to Rule 13d-1(c)) By signing below each Reporting Person certifies that, to the best of its knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and not held in connection with or as a participant in any transaction having that purpose or effect.

Schedule 13G PAGE 12 OF 12 SIGNATURES After reasonable inquiry and to the best of our knowledge and belief, the undersigned certify that the information set forth in this statement is true, complete and correct. DATED: August 5, 2005 /s/ O. Andreas Halvorsen O. ANDREAS HALVORSEN, individually, and as a Member of VIKING GLOBAL PERFORMANCE LLC, on behalf of itself and VIKING GLOBAL EQUITIES LP, and as a Managing Director of Viking Global Partners LLC, on behalf of VIKING GLOBAL INVESTORS LP. /s/ Brian T. Olson, individually BRIAN T. OLSON /s/ David C. Ott, individually DAVID C. OTT 2078839.1