Several experimental studies have demonstrated that certain steroid hormones can induce differentiation of mouse myeloid leukemic cells to macrophages and granulocytes. We have shown that high-dose methylprednisolone treatment (HDMP, 20-30 mg/kg/day) can induce differentiation of leukemic cells to mature granulocytes in children with different morphological subtypes of acute myeloblastic leukemia (FAB AML M1, M2, M3, M4). In addition, apoptosis can also be induced in vivo and in vitro in AML blast by HDMP treatment. Short-course (3 to 5 days) HDMP treatment increases the hematopoietic CD34-positive progenitor cells in both bone marrow and peripheral blood in children with AML. Acceleration of leukocyte and neutrophil recovery has been obtained by the administration of short-course HDMP in chemotherapy-induced neutropenic children with AML. The addition of HDMP to antileukemic chemotherapy increased the complete remission rate and prolong ed the duration of remission in children with AML and significantly improved the outcome of AML children who presented with extramedullary infiltration. We suggest that the possibility of HDMP-induced differentiation and apoptosis should be evaluated in patients with other malignant diseases.