Abstract: The use of radioprotectors such as WR-2721 in radioactive phosphorous is interested because radiation delivered to tumor organ therapy can induce side effects in the bone marrow and most normal organs. To evaluate the potential of WR-2721, we treated mice with this drug (400 mg kg-1) prior administration of 32P at dose 4 μCi g-1 intraperitoneally. We determined hematological parameters in treated mice with 32P or WR-2721+32P at twenty days after treatment. Administration of radioprotector failed to enhance RBC, WBC, PLT, Hb and Hct from 32P. In contrast, this radioprotector provided significant protection from total-body gamma irradiation with a DRF 1.91. These results suggest that the potential role of WR-2721 in a 32P therapy is limited because of the difficulty in achieving continuous protection with a single dose of this drug due to its short half-life.