Effect of corticosteroids (steroids) on some hemostatic parameters was serially studied in 23 children with minimal change nephrotic syndrome (MCNS). Increased platelet count, erythrocyte sedimentation rate (ESR), cholesterol, fibrinogen, fibrin(ogen) degradation products (FDP), alpha 2-macroglobulin (alpha 2M), alpha 2-antiplasmin (alpha 2AP) and protein C, and reduced antithrombin III (ATIII) and plasminogen (Plg) were noted in relapse before steroid therapy began. With institution of oral prednisolone, FDP started to fall, and platelet count, cholesterol, alpha 2M, ATIII, Plg, alpha 2AP and protein C started to increase despite unchanged nephrotic state from that before the therapy. In remission induced by prednisolone, platelet count, cholesterol, alpha 2M, ATIII, Plg, alpha 2AP and protein C were still increased, but normalized off therapy. ESR, fibrinogen, FDP, alpha 2M and protein C correlated inversely with serum albumin and directly with cholesterol and urine protein excretion. In contrast, ATIII and Plg correlated directly with serum albumin and inversely with cholesterol and urine protein excretion. A direct correlation was only noted between alpha 2AP and the dose of prednisolone. The data indicate that steroids appear to be a thrombogenic factor by accerelating thrombocytosis and hyperlipidemia, and by reducing plasma fibrinolysis in children with MCNS.