Forty one patients with recently recognised bronchial asthma were studied. Activity of plasminogen activator inhibitor (PAI-1), platelet adhesion and aggregation, antigens of tissue and urokinase plasminogen activators (respectively, t-PA Ag and u-PA Ag), euglobulin lysis time (ELT), complexes of plasmin-antiplasmin (PAP) and fibrin degradation products (FDP) were tested before and after fourteen days administration of 20-30 mg/d prednisone. Statistical significant increase of PAI-1 activity, on the average about 75%, was found (8.35+/-9.38 U/ml before, and 14.6+/-13.3 U/ml after treatment; p< 0.02). In 31 asthmatic patients (75.6%), after prednisone treatment, increased of PAI-1 activity together with platelet adhesion and aggregation were observed. Among other studied fibrinolysis factors no statistical significant differences before and after treatment were found. These results suggest that in asthmatic patients after prednisone treatment raises PAI-1 activity, probability because of releasing of the increased amount of PAI-1 from activated platelet.