In order to investigate the effects of short term high dose methylprednisolone (HDMP) on fibrinolytic system in patients with ALL, 16 of newly diagnosed 32 ALL patients were given HDMP alone (20 mg/kg per day) for 5 days and the rest 16 patients received conventional dose methylprednisolone (CDMP, 2 mg/kg per day) prior to a combination chemotherapy consisting of methylprednisolone, vincristin, daunorubicin and 9 doses Of L-Asparaginase. Fibrinogen levels decreased in both groups at day 5 which was statistically significant in the HDMP group. Baseline D-dimer levels of both groups were significantly higher than those of the control group including 24 healthy children. D-dimer levels significantly decreased after initiation of combination therapy in both groups. There was a significant rise in PAI-1 levels after combination therapy both in HDMP and CDMP groups. (C) 2003 Elsevier Ltd. All rights reserved.