The authors compare the apoptotic effect on the lymphoblasts and the proliferative effect on the myeloid lineage cells of a short-course high-dose methylprednisolone ( HDMP) and the conventional-dose prednisolone treatments in children with acute lymphoblastic leukemia ( ALL). The patients were divided into 2 groups. Group I ( n = 10) received HDMP ( 30 mg/kg/day for 7 days) in a single dose before 6 a. m. perorally. Group II ( n = 10) received prednisolone ( 2 mg/kg/ day for 7 days) in 3 doses. The apoptotic percentages of lymphpblasts and the percentages of blasts and myeloid lineage cells were determined after performing the bone marrow aspiration ( BMA) at diagnosis on the 0th, 3rd, and 7th days of the treatments in all patients. The mean apoptotic percentages of the lymphoblasts on the 3rd day were significantly higher than those on the 0th and 7th days in both groups ( p <.05). The highest apoptosis was determined on the 3rd day in group I. The mean percentages of the blast cells on the 7th day were significantly lower than those on the 0th and the 3rd days in both groups ( p <.05). The lowest lymphoblast percentage was determined on the 7th day in group I. The mean percentages of the CD13+ and CD33+ cells on the 7th day were significantly higher than those on the 0th and the 3rd days in both groups ( p <.05). The highest percentages of the CD13+ and CD33+ cells were found on the 7th day in group I. Prednisolone and HDMP showed no proliferative effect on the CD14+ cells. These findings indicate that a short-course HDMP treatment shows a more effective apoptosis on the lymphoblasts and on the increase of the myeloid lineage cells when compared to the prednisolone treatment. The authors suggest that HDMP may be used in the treatment of patients with ALL instead of prednisolone.