SecProbe.io

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                                  June 6, 2005

Securities and Exchange Commission
Division of Corporation Finance
450 Fifth Street, N.W.
Washington, D.C.  20549
Attention:  Jeffrey Riedler, Esq.

              Re:       Callisto Pharmaceuticals, Inc.
                        Form S-3 filed April 5, 2005
                        File No. 333-123863

Dear Mr. Riedler:

     This letter sets forth the responses of Callisto  Pharmaceuticals,  Inc., a
Delaware  corporation (the "Company" or "we"), to the comments received from the
Staff (the "Staff") of the Securities and Exchange Commission (the "Commission")
by letter dated April 29, 2005 concerning the Company's  Registration  Statement
on Form S-3 (File No.  333-123863)  filed with the  Commission  on April 5, 2005
(the "Registration Statement").  We are authorized by the Company to provide the
responses contained in this letter on behalf of the Company.

     The numbers of the  responses in this letter  correspond  to the numbers of
the Staff's  comments as set forth in its letter to the Company  dated April 29,
2005.  References  in the text of the  responses  herein  to  captions  and page
numbers are to Amendment  No. 1 to Form S-3 or to Form 10-K/A for the year ended
December 31, 2004, as applicable,  both of which are being filed  herewith.  For
your  convenience,  we set forth each comment  from your comment  letter in bold
type-face and include the Company's response below it.

GENERAL

1.   PLEASE NOTE THAT WHERE WE PROVIDE EXAMPLES TO ILLUSTRATE WHAT WE MEAN BY
     OUR COMMENTS, THEY ARE EXAMPLES AND NOT EXHAUSTIVE LISTS. IF OUR COMMENTS
     ARE APPLICABLE TO PORTIONS OF THE FILING THAT WE HAVE NOT CITED AS
     EXAMPLES, MAKE THE APPROPRIATE CHANGES IN ACCORDANCE WITH OUR COMMENTS.

     Where applicable, we have made changes in accordance with your comments
     throughout Amendment No. 1 to Form S-3 and Form 10-K/A.

2.   WE NOTE THAT YOUR 10-KSB INDICATES THAT YOUR PUBLIC FLOAT EXCEEDS $40
     MILLION. PLEASE PROVIDE US WITH AN ANALYSIS SUPPORTING THE COMPANY'S
     DECISION TO FILE A FORM 10-KSB INSTEAD OF A 10-K. WE NOTE THAT THE FLOAT
     DISCLOSED ON THE PRIOR 10-K WAS NEARLY $70 MILLION.
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     We have converted the Form 10-KSB to a Form 10-K for the year ended
     December 31, 2004.

3.   PLEASE INCLUDE PAGE NUMBERS ON THE FILING.

     We have included page numbers on Amendment No. 1 to Form S-3.

FORM S-3
SUMMARY

4.   PLEASE CONSIDER PRESENTING THIS INFORMATION USING MORE SIMPLE LANGUAGE THAT
     INVESTORS WILL UNDERSTAND. AS A FEW EXAMPLES ONLY, TERMS SUCH AS
     "OSTEOLYTIC BONE DISEASE," "ANTHRACYCLINE," "REFRACTORY," AND SIMILARLY
     COMPLEX TERMS SHOULD BE REPLACED WITH MORE SIMPLE TERMS OR DEFINED THE
     FIRST TIME THEY ARE USED SO THAT INVESTORS CAN EASILY UNDERSTAND YOUR
     DISCLOSURE. PLEASE REVIEW THE SECTION AND THE RISK FACTORS AND REVISE THE
     SECTION ACCORDINGLY.

     Throughout the Summary section of Amendment No. 1 to Form S-3 and Form
     10-K/A we have replaced or defined complex terms.

5.   WE NOTE YOUR USE OF THE TERM "PHASE I/II" REGARDING YOUR RECENTLY COMPLETED
     AND CURRENTLY ONGOING CLINICAL TRIALS REGARDING YOUR TWO RESPECTIVE
     PRODUCTS. THE USE OF THE TERM "PHASE I/II" SHOULD ONLY BE USED IF YOUR
     TRIAL MET ALL THE FDA REQUIREMENTS FOR A PHASE II STUDY. PLEASE TELL US
     WHETHER OR NOT YOUR PHASE I/II TRIAL MET ALL OF THE REQUIREMENTS OF PHASE
     II CLINICAL TRIALS. WE NOTE THAT PHASE II TRIALS TYPICALLY INVOLVE
     ADMINISTERING THE PRODUCT UNDER DEVELOPMENT TO 100-300 PARTICIPANTS,
     ALLOWING FOR THE EVALUATION OF THE EFFECTIVENESS OF THE DRUG AND
     DETERMINING THE SHORT-TERM SIDE EFFECTS AND RISKS. HAS THE FDA AGREED THAT
     YOUR RESPECTIVE STUDIES WERE DESIGNED TO MEET THE REQUIREMENTS OF PHASE II
     TRIALS? FOR ANY OF YOUR STUDIES NOT DESIGNED TO MEET ALL REQUIREMENTS OF
     FDA APPROVED PHASE II CLINICAL TRIALS, PLEASE DELETE THE REFERENCES TO
     "PHASE I/II," REPLACE THE REFERENCES WITH THE TERM "PHASE I" AND EXPLAIN
     THAT THE TRIALS ARE DESIGNATED TO PROVIDE INFORMATION RELATED TO THE
     EFFICACY, NOT THE EFFECTIVENESS, OF THE PRODUCT CANDIDATE. THIS COMMENT
     ALSO APPLIES TO YOUR REFERENCES TO "PHASE II/III" THROUGHOUT THE
     PROSPECTUS.

     The use of the term "Phase I/IIa" is unique to cancer trials where an
     experimental drug entering the clinic is immediately evaluated in cancer
     patients rather than in healthy volunteers which is the case for other
     disease indications. Consequently, in cancer trials, the term "Phase I/IIa"
     is used rather than "Phase I" which is the designation for an initial
     safety trial in the clinic. A Phase I/IIa cancer trial has the potential to
     pick up an early indication of a drug effect which is something that is
     normally assessed in a Phase II trial in other diseases. The ongoing
     Atiprimod clinical trial in relapsed multiple myeloma patients qualifies as
     a Phase I/IIa trial, by these criteria. The protocol was reviewed by the
     FDA and by the institutional review boards of the clinical institutions
     where the
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     clinical trial is being held. As stated on page 5 of Form 10-K/A under
     "Development Strategy" the primary objective of the clinical study is to
     assess the safety of the drug and the secondary objective is to measure the
     pharmacokinetics, evaluate the response in patients with refractory disease
     and to identify possible surrogate responses to the drug to better
     determine the mechanism of drug action. Therefore, the Atiprimod clinical
     trial's objectives are to assess the safety as well as some efficacy of the
     drug which is why it is a Phase I/IIa clinical trial.

     The earlier trial of Annamycin also qualifies as a Phase I/IIa trial as it
     was conducted in relapsed leukemia patients, and in fact, data were
     reported on complete remissions in this study, which is an effect that
     exemplifies the Phase IIa portion of the Phase I/IIa trial.

     We do not refer to a Phase II/III trial designation in Amendment No. 1 to
     Form S-3 or in Form 10-K/A since no such designation exists in clinical
     development.

RECENT DEVELOPMENTS

6.   PLEASE EXPLAIN WHAT YOU MEAN BY "IRB APPROVAL."

     In Recent Developments in Amendment No. 1 to Form S-3 on page 6, we have
     defined IRB approval as Institutional Review Board approval.

RISK FACTORS

7.   WHEN DISCLOSING A RISK FACTOR, YOU SHOULD CUSTOMIZE IT WITH SPECIFIC
     REASONS WHY YOU MAY BE EXPOSED TO A PARTICULAR RISK SO AS TO MAKE THE
     DISCLOSURE MORE MEANINGFUL. AS ONE EXAMPLE ONLY, THE DISCLOSURE IN "IF OUR
     AGREEMENTS WITH ANORMED oR THE UNIVERSITY OF TEXAS.. .," YOU SHOULD EXPAND
     AND CUSTOMIZE THE RISK FACTOR TO DISCLOSE WHETHER THERE ARE ANY FACTS OR
     CIRCUMSTANCES THAT COULD CAUSE YOU TO MISS A PAYMENT OR OTHERWISE HAVE
     EITHER OF THESE AGREEMENTS TERMINATED, RATHER THAN GENERICALLY REFERRING TO
     THEIR POSSIBLE TERMINATION BECAUSE OF A MISSED PAYMENT.

     PLEASE REVIEW ALL OF YOUR RISK FACTORS TO ENSURE THAT YOUR DISCLOSURE IS
     CUSTOMIZED FOR THE COMPANY AND IS AS SPECIFIC AS POSSIBLE. IN YOUR RESPONSE
     LETTER, PLEASE IDENTIFY ALL PLACES WHERE REVISIONS ARE MADE IN RESPONSE TO
     THIS COMMENT.

     We have reviewed all of our risk factors to ensure that our disclosure is
     customized and is as specific as possible. The following risk factors have
     been modified in response to this comment.

     "If our agreements with AnorMED Inc. or the University of Texas .....".

     "Delays in clinical testing .....".

     "If our product candidates are unable to compete effectively ......".

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     "If our relationships with our contract manufacturer for Annamycin .....".

     "We will need to increase the size of our organization .....".

     "It is difficult and costly to protect our proprietary rights ......".

8.   IN YOUR HEADING, PLEASE ELIMINATE THE SENTENCE "THE RISKS DESCRIBED BELOW
     ARE NOT THE ONLY ONES AFFECTING US." ALL MATERIAL RISK FACTORS SHOULD BE
     DISCLOSED.

     In the heading to Risk Factors in Amendment No. 1 to Form S-3 on page 7 we
     have deleted the sentence "the risks described below are not the only ones
     affecting us."

"WE HAVE INCURRED SIGNIFICANT LOSSES..."

9.   PLEASE UPDATE YOUR FINANCIAL DATA IN THIS RISK FACTOR TO INCLUDE NUMBERS
     FOR THE FIRST QUARTER OF THIS YEAR.

     Such risk factor in Amendment No. 1 to Form S-3 on page 7 has been updated
     to include financial data for the quarter ended March 31, 2005.

"WE WILL NEED TO RAISE SUBSTANTIAL ADDITIONAL CAPITAL.."

10.  PLEASE DISCLOSE THE AMOUNT OF CASH YOU EXPEND ON A MONTHLY BASIS. IF THERE
     IS A SIGNIFICANT VARIABILITY, PLEASE INCLUDE A RANGE.

     Such risk factor in Amendment No. 1 to Form S-3 and Form 10-K/A on page 8
     and 10, respectively, has been modified to disclose the amount of cash
     expended in 2004 and on a monthly basis during 2004 which is an average.

"DELAYS IN CLINICAL TESTING. . ."

11.  PLEASE DISCLOSE ANY DELAYS YOU HAVE EXPERIENCED IN CLINICAL TRIALS TO THIS
     POINT.

     Such risk factor has been modified in Amendment No. 1 to Form S-3 and Form
     10-K/A on page 9 and 11, respectively.

"THE COMMERCIAL SUCCESS OF OUR PRODUCTS..."

12.  TO THE EXTENT THAT THERE ARE FACTS OR CIRCUMSTANCES THAT WOULD SUPPORT THE
     CONCERNS SET FORTH IN THE BULLET POINTS IN THIS SECTION, PLEASE DISCLOSE
     THOSE FACTS IN THIS RISK FACTOR.

     We have removed this risk factor because our lead drug candidates are
     targeting cancers that have no "standard of care." In the event our lead
     drug candidates are approved we anticipate the concerns set forth in this
     risk factor will not be a material risk to the Company.

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"IF OUR PRODUCT CANDIDATES ARE UNABLE TO COMPETE EFFECTIVELY.."

13.  IF THERE ARE ANY PRODUCTS ON THE MARKET OR IN DEVELOPMENT THAT WOULD BE
     COMPETITIVE WITH YOUR PRODUCTS, PLEASE DESCRIBE THOSE PRODUCTS AND DISCLOSE
     ANY ADVANTAGES THAT THOSE PRODUCTS MIGHT HAVE RELATIVE TO YOUR PRODUCTS.

     Such risk factor has been modified in Amendment No. 1 to Form S-3 and Form
     10-K/A on page 10 and page 11, respectively.

"WE MAY NEED OTHERS TO MARKET AND COMMERCIALIZE OUR PRODUCT CANDIDATES..

14.  PLEASE DISCLOSE IF YOU HAVE ANY CURRENT PLANS TO ENTER INTERNATIONAL
     MARKETS.

     Such risk factor has been modified in Amendment No. 1 to Form S-3 and Form
     10-K/A on page 11 and page 12, respectively, to state that we have no
     current plans to enter international markets.

"IF THE FDA DOES NOT APPROVE OUR CONTRACT MANUFACTURERS' FACILITIES. . ." "WE
RELY UPON THIRD PARTIES TO CONDUCT CLINICAL TRIALS..."

15.  CURRENTLY, THIS RISK FACTOR DESCRIBES THE POTENTIAL PROBLEMS ASSOCIATED
     WITH COLLABORATIONS. HOWEVER, IF THE COMPANY IS CURRENTLY DEPENDENT UPON
     COLLABORATORS IN A MATERIAL WAY (SUCH AS THE THIRD PARTY MANUFACTURERS AND
     CLINICAL TRIAL PROVIDERS YOU DESCRIBE IN A SUBSEQUENT RISK FACTOR), THIS
     RISK FACTOR SHOULD ALSO DISCUSS THE RISKS ASSOCIATED WITH THAT DEPENDENCE.
     YOU SHOULD DESCRIBE THE SPECIFIC COLLABORATION UPON WHICH YOU ARE DEPENDENT
     SO THAT INVESTORS CAN UNDERSTAND THE DEPENDENCE AND THE RISKS ASSOCIATED
     WITH LOSING THE COLLABORATION. YOU SHOULD ALSO DESCRIBE THE ALTERNATIVES
     THE COMPANY WOULD FACE IF THE COLLABORATION WERE LOST.

     In Amendment No. 1 to Form S-3 and Form 10-K/A on page 12 and 13,
     respectively, we have added a risk factor regarding our dependence on the
     manufacturer of Annamycin which discusses the risks associated with that
     dependence as well as the alternatives we would face if the collaboration
     was lost.

"IF WE FAIL TO ATTRACT AND KEEP SENIOR MANAGEMENT.."

16.  TO THE EXTENT THAT YOU HAVE EXPERIENCED PROBLEMS ATTRACTING AND RETAINING
     KEY PERSONNEL IN THE RECENT PAST, PLEASE REVISE TO DESCRIBE THESE PROBLEMS.
     ADDITIONALLY, IF ANY KEY EMPLOYEE HAS PLANS TO RETIRE OR LEAVE YOUR COMPANY
     IN THE NEAR FUTURE, PLEASE REVISE THE DISCUSSION TO DISCLOSE THIS
     INFORMATION.

     To date we have not experienced problems attracting and retaining key
     personnel. We are not aware of any key employee planning to retire or leave
     our company in the near future.

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"IF WE FAIL TO ACQUIRE AND DEVELOP.."

17.  PLEASE DISCLOSE WHETHER ACQUISITIONS ARE A MATERIAL COMPONENT OF YOUR
     BUSINESS MODEL OR BUSINESS STRATEGY AND ALSO DISCLOSE WHETHER THE COMPANY
     HAS ANY CURRENT INTENTIONS TO ACQUIRE ANOTHER COMPANY.

     Such risk factor has been modified in Amendment No. 1 to Form S-3 and Form
     10-K/A on page 13 and 14_, respectively, to state that as part of our
     growth strategy in addition to developing our product candidates, we intend
     to license or acquire additional products and product candidates. We also
     state that we have no current intentions to acquire another company.

"WE WILL NEED TO INCREASE THE SIZE OF OUR ORGANIZATION.."

18.  PLEASE DISCLOSE THE NUMBER OF NEW EMPLOYEES THAT THE COMPANY PLANS TO HIRE
     TO FULFILL ITS STRATEGY FOR THE NEXT TWO YEARS.

     Such risk factor has been modified in Amendment No. 1 to Form S-3 and Form
     10-K/A on page 14 and 15, respectively, to disclose the approximate number
     of employees the Company plans to hire over the next year. The Company was
     uncomfortable forecasting a number beyond one year since the determination
     is dependent on the progress of the Company's development activities and
     clinical trials as well as financing of the Company.

19.  IN ADDITION, YOU INDICATE THAT YOU WILL BROADEN EXPERTISE AND EXTEND
     MANUFACTURING CAPABILITIES. PLEASE EXPAND THIS DISCUSSION TO DISCLOSE
     SPECIFICALLY WHAT YOUR P1ANS ARE IN THESE REGARDS.

     We do not have any plans to broaden expertise and develop or extend
     manufacturing capabilities.

"RISKS RELATED TO OUR INTELLECTUAL PROPERTY"

20.  WITH RESPECT TO YOUR CONCERNS REGARDING INTELLECTUAL PROPERTY, PLEASE
     DISCLOSE WHAT INTELLECTUAL PROPERTY THAT YOU POSSESS AND ANY SPECIFIC
     CONCERNS THAT YOU MAY HAVE, EITHER WITH REGARD TO INVALIDATION OR CLAIMS
     THAT YOU HAVE INFRINGED UPON THE RIGHTS OF OTHERS.

     Such risk factor in Amendment No. 1 to Form S-3 and Form 10-K/A on page 15
     and 16, respectively, has been modified to disclose our intellectual
     property. We currently do not have any specific concerns either with regard
     to invalidation or claims the we have infringed upon the rights of others.

21.  PLEASE DISCLOSE WHEN YOUR MATERIAL PATENTS WILL EXPIRE.

     Such risk factor in Amendment No. 1 to Form S-3 and Form 10-K/A on page 15
     and 16, respectively, has been modified to state when our material patents
     will expire.

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RISKS ASSOCIATED WITH OUR COMMON STOCK
"WE ARE AT RISK OF SECURITIES CLASS ACTION LITIGATION"

22.  TO THE EXTENT THAT THERE ARE ANY FACTS OR CIRCUMSTANCES THAT MIGHT INDICATE
     THAT A PARTY IS CONSIDERING BRINGING A CLASS ACTION SUIT AGAINST THE
     COMPANY OR IF ONE HAS BEEN FILED, DISCLOSE THOSE FACTS IN THIS RISK FACTOR.

     We are not aware of any facts or circumstances that might indicate that a
     party is considering bringing a class action suit against the Company.

SELLING SECURITYHOLDERS

23.  WE CALL TO YOUR ATTENTION THE REQUIREMENTS OF FORM S-3 WITH RESPECT TO THE
     INFORMATION REQUIRED BY ITEM 507 (SELLING SHAREHOLDERS). WE NOTE THAT
     CERTAIN ENTITIES LISTED AS SELLING SHAREHOLDERS IN THE SELLING
     SECURITYHOLDER TABLE MAY BE BROKER-DEALERS THAT HAVE OBTAINED THE SHARES
     OTHER THAN AS COMPENSATION FOR SERVICES. IN THAT EVENT, SUCH SELLING
     SHAREHOLDERS ARE DEEMED UNDERWRITERS UNDER THE SECURITIES ACT OF 1933. IN
     THAT CASE, PLEASE REVISE YOUR REGISTRATION