Experiments of mice F1(CBAx57BL) were made to study cyclophosphamide effects on the number of circulating neutrophil granulocytes (NG) and on their main functions (receptor, phagocytic, function of microbicidal systems). NG count, the number of NG carrying receptors to sheep red cells, complementary EAC=POH, phagocytic and digestive activities and NBT-test were measured 15 and 60 min after administration of small (0.5 mg/kg) and large (150 mg/kg) doses of cyclophosphamide. The results suggest clear dose- and time-related effect of the drug which can induce both depression and stimulation. The data obtained can be utilized in developing approaches to prevention of complications caused by NG dysfunctions in immunosuppressive therapy of tumors, lymphoproliferative diseases, organ and tissue transplantation.