Fibrinolytic activity was studied in 51 patients subjected to major surgery (27 urological and 24 gynecological) without prophylaxis. Postoperative deep-vein thrombosis (DVT) was diagnosed by venography in 6 patients (11 %). Blood samples were obtained preoperatively and on days 1, 3 and 7 postoperatively. Reduced fibrinolytic activity, as determined by prolongation of euglobulin lysis time (ELT), decrease in plasminogen activators on fibrin plate and decrease in tissue-type plasminogen activator (t-PA) activity were present postoperatively. Moreover, a marked increase in short duration in fast-acting inhibitor (PA-inhibitor) levels was observed on postoperative day 1 (p < 0.001). Patients with DVT had higher fibrinogen degradation product (FDP) levels on postoperative days 3 and 7 (p < 0.02). Preoperative PA-inhibitor activity was higher (p < 0.02) in those patients who developed postoperative DVT. It is concluded that the decrease in t-PA and the increase in PA-inhibitor may contribute to the reduced postoperative fibrinolytic activity after major surgery. PA-inhibitor may represent a useful predictive marker of postoperative DVT.