The experimental and clinical studies were carried out to alleviate the bone marrow suppression by antineoplastic drugs. Faster recovery of granulopoiesis was observed by pretreating recipients with RBC hypertransfusion and/or OK-432 (Picibanil, biological products of beta-streptococci.) In experimental mice, higher granulocyte counts could be maintained with hypertransfusion in the peripheral blood, and the recovery of granulopoietic series and CFU-S of bone marrow cells were found to be more rapid after cyclophosphamide administration. OK-432 also resulted in higher peripheral granulocyte, whereas the total nucleated cell counts and CFU-S were decreased in the bone marrow, suggesting sparing bone marrow granulocyte reserve and its migration to the peripheral blood. The mechanism of higher granulocyte count after hypertransfusion was not clearly explained but it was considered that erythroid suppression caused colateral flow of multipotential stem cells to granulopoiesis. The effect of both combinations was unexpectedly less significant in the recovery of granulopoiesis, but it was thought that the optimal time interval should be sought between pretreatment and the administration of anti-neoplastic agents. The clinical use of hyper transfusion and OK-432 also proved the alleviation of granulocytopenia, and rapid granulocyte recovery at the time of consolidation therapy among children with AML.