The proposed prospective, controlled study will examine the prevalence of postoperative thromboembolic disease (TED) following total hip replacement (THR) in patients without prior TED. Two treatment regimes will be compared to the control group, namely first, aspirin given pre-and postoperatively and second, aspirin and the concomitant use of external pnuematic compression (EPC) of the calf before, during and after operation. Thrombus detection will be by I125 fibrinogen scan technique, cuff impedance phlebography, plethysmography and radiographic phlebography. The postoperative inhibition of the fibrinolytic system will be studied, and the ability of EPC to reduce this inhibition will be compared to the effects occurring in the control group and those receiving aspirin alone. The objectives are: 1) to evaluate the efficacy of aspirin as a prophylactic agent compared to a control group; 2) to determine if the addition of EPC enhances the effect of aspirin alone; and 3) to study the fibrinolytic system in relation to postoperative changes therein, to correlate those with thrombus formation and to investigate alterations of these changes by EPC.