The fibrinolytic system was studied in 30 patients undergoing elective cholecystectomy and in 30 with more advanced elective abdominal surgery. Blood was sampled before, during and after operation for determination in plasma of the tissue plasminogen activator (t-PA), the recently described fast t-PA inhibitor, and plasmin alpha 2-antiplasmin complex (PAP). In addition the t-PA activity during venous occlusion was determined preoperatively. Most of the patients showed raised t-PA levels during surgery, but the interindividual variation was wide and was not correlated to fibrinolytic capacity measured preoperatively as enhancement of t-PA activity during venous occlusion. The levels of the t-PA inhibitor rose during and immediately after surgery, and were higher in patients without increased t-PA activity during surgery. The patients with more advanced disease had higher levels of the inhibitor than the cholecystectomy patients. The data suggest that the t-PA inhibitor may influence the fibrinolytic response to surgical trauma and may explain the previously reported shutdown in fibrinolysis in the early postoperative period. PAP, used as reflecting the overall fibrinolytic activity, was increased in plasma after the first postoperative days.