Specific inhibition of thrombin is a new method for the prevention of postoperative deep-vein thrombosis. The objective of this multicenter, randomized, double-blind study was to compare the efficacy and safety of desirudin (Revasc, CGP 39393; fifteen milligrams two times a day) with that of unfractionated heparin (5000 international units three times a day) in patients having a primary elective total hip replacement. The medications were administered subcutaneously, starting preoperatively and continuing for eight to eleven days. The primary end point was a confirmed thromboembolic event during the treatment period. The presence of deep-vein thrombosis was evaluated with bilateral venograms, which were centrally assessed by two independent radiologists.A total of 445 eligible patients were randomized: 220, to management with heparin, and 225, to management with desirudin. A per-protocol analysis of efficacy was performed for the 351 patients (79 per cent) for whom an adequate bilateral venogram had been made within eight to eleven days after the operation or who had had a proved thromboembolic event. The prevalence of confirmed deep-vein thrombosis was thirteen (7 per cent) of 174 patients who had received desirudin and forty-one (23 per cent) of 177 patients who had received heparin, a significant difference (p < 0.0001). The prevalence of proximal deep-vein thrombosis was also significantly reduced (p < 0.0001), by 79 per cent, in the group that had received desirudin (six [3 per cent] of 174 patients) compared with in the group that had received heparin (twenty-nine [16 per cent] of 177). There were no confirmed pulmonary embolisms or deaths during the period of prophylaxis. During a six-week follow-up period, pulmonary embolism was confirmed in four patients, all of whom had received heparin. There was no significant difference between the treatment groups with respect to bleeding variables or bleeding complications.These data demonstrate that a fixed dose of fifteen milligrams of desirudin, started preoperatively and administered subcutaneously twice daily for at least eight days, provided effective, safe prevention of thromboembolic complications, with no specific requirements for laboratory monitoring, in patients who had a total hip replacement.