Coagulation activation markers were studied in 148 patients undergoing total hip replacement under recombinant-hirudin (Desirudin, Revasc) prophylaxis with the aim of investigating the efficacy and safety of this anticoagulant compared with heparin in terms of biological effects on coagulation variables and bleeding. Hirudin (10, 15 or 20 mg s.c. b.i.d.) or unfractionated heparin (5000 IU s.c. t.i.d.) was administered immediately before surgery and continued for 8-12 days. Activated partial thromboplastin time (aPTT), prothrombin activation fragment F1 + 2 (F1 + 2), thrombin-antithrombin III complexes (TAT) and D-dimer were measured at baseline and on postoperative days 1,3 and 6, immediately before the morning injection. In comparison with baseline values, heparin had little effect on aPTT whereas the three hirudin doses prolonged aPTT significantly with no differences among the three doses. Moreover, there were no group differences in perioperative or cumulative blood loss or transfusion requirements. F1 + 2 fragment, TAT and D-dimer plasma levels were higher than at baseline during the entire postoperative period, with different trends (F1 + 2 increasing, TAT decreasing, D-dimer increasing, decreasing and then increasing again), but without significant differences among the four treatment groups. Our findings suggest that specific inhibition of thrombin seems a safe and efficacious mode of blocking thrombin activity after hip surgery although it does not prevent thrombin generation.