Since the differentiating effect of high-dose methylprednisolone (HDMP) on myeloid leukemic cells has been shown in one of our patients with acute myeloblastic leukemia (AML-M4), 27 previously untreated children with AML were given HDMP (20-30 mg/kg per day) combined with cytosine arabinoside (Ara-C; 3 mg/kg) for the first 2 weeks of induction therapy. Marked clinical improvement was observed in all patients with the exception of one who died within 24 hours of the treatment. Enlarged liver and spleen (greater than 5 cm) became nonpalpable in 3 (37%) out of 8 and 5 (100%) out of 5 patients, respectively, and bone marrow blasts decreased below 5% in 7 patients (27%) within 2 wk of HDMP and Ara-C treatment. Adriamycin (1 mg/kg) was added 2 wk after initiation of induction therapy. Twenty-two (84.6%) of the 26 patients achieved complete remission, 3 (11.5%) had partial remission and no response was obtained in one. Treatment was well tolerated. The addition of HDMP as a differentiating and/or cytolytic agent to conventional anti-leukemic chemotherapy increased the complete remission rate and prolonged the duration of remission of our AML patients.