Exhibit 23 Consent of Independent Registered Public Accounting Firm -------------------------------------------------------- Callisto Pharmaceuticals, Inc. New York, New York We hereby consent to the incorporation by reference in the Registration Statement on Form S-8 (No. 333-119648) of Callisto Pharmaceuticals, Inc. and subsidiaries of our report dated March 14, 2005, relating to the consolidated financial statements which appear in this Form 10-K/A. /s/ BDO Seidman, LLP BDO Seidman, LLP New York, NY June 3, 2005