As an antitumor agents cyclophosphamide (CPA) is frequently used in animal clinic. Important adverse effects of its administration are leukopenia, thrombocytopenia and anemia. We investigated the effects of chicken egg white derivatives (EWD and EF-203) on the changes of blood cells and the neutrophil phagocytosis of rats administered with CPA. Rats were administered CPA peritoneally at dose of 50 mgag once a day far 3 days plus either EWD or EF-203 orally at dose of 200 mg/kg once a day far 3 days. Thereafterl the changes of blood cells by automatic blood cell counter and the phagocytosis of neutrophils by flow cytometry were examined far 7 days. There was no change in RBC values regardless of administration of either EWD or EF-203 throughout experimental period. But rats receiving CPA plus either EWD or EF-203 showed a significant higher PCV values than those of CPA alone (p<0.01). The numbers of peripheral blood platelets and WBC and the differential count of neutrophils in the ra% receiving CPA plus either EWD or EF-203 were significantly higher (p<0.05 to 0.01) than those of CPA alone. Moreover, these rats showed significanly enhanced phagocytoses of neutrophils when compared to rats with CPA alone (p<0.01). These result suggested that chicken egg white derivatives including EWD and EF-2% have immunomodulatory effects in regard to the increase of platelets, WBC, differential count of neutrophils, PCV, and the enhancement of phagocytic activity of neutrophils in immunosuppressed rats by CPA. Thus, co-adminstration of chicken egg white derivatives will be able to reduce the side effects in the animals treated with antitumor agents.