Without prophylaxis, patients subjected to major abdominal surgery have a risk of deep vein thrombosis of approximately 30%, while the rate varies between 40% and 60% in orthopedic surgery. The reasons for this discrepancy are not completely understood. The present study was designed to compare the pre-and postoperative behavior of different coagulation and fibrinolysis parameters in patients undergoing both types of surgery, receiving low molecular weight heparin prophylaxis. Samples were taken before operation and on postoperative days 1,3, and 7. The following parameters were assessed: prothrombin fragment 1+2, thrombin-antithrombin III complexes, fibrinopeptide A, tissue plasminogen activator, plasminogen activator inhibitor, plasmin-c~__-antiplasmin complexes, and fibrin degradation products. We found a significant increase in the clotting markers postoperatively compared with preoperative values (P<0.05), both in abdominal and orthopedic surgery, indicating a marked hemostatic activation which remained until postoperative day 7. A significant increase in plasminogen activator inhibitor (P<0.01) and a decrease in tissue plasminogen activator and plasmin-%-antiplasmin complexes was also observed early