Soluble fibrin complexes, fibrin degradation products, and anti-thrombin III levels were determined in the plasma of 20 patients undergoing elective total hip replacement. The presence of deep venous thrombophlebitis was determined by venography at the end of the first postoperative week. Patients who developed thrombosis exhibited impairment of fibrinolysis as de-Patients who developed thrombosis exhibited impairment of fibrinolysis as detected levels of anti-thrombin III and soluble fibrin complexes were not useful in indicating the presence of deep venous thrombosis. However, the preoperative level of soluble fibrin complexes closely correlated with the subsequent development of thrombosis. Elevated soluble fibrin complexes appear to identify a group of patients with activated coagulation systems who are prone to develop thrombosis during total hip replacement.