The aim of this study was to measure the coagulation inhibitors in two groups of uremic patients treated with hemodialysis (HD) and continuous ambulatory peritoneal dialysis (CAPD) to evaluate the differences in anticoagulant activity. In 20 patients on HD and 20 on CAPD, mean age 66 +/- 8 and 58 +/- 14 years, respectively, the following parameters were determined between dialysis exchanges: protein C (PC), protein S (PS), antithrombin III (AT III), electrophoresis, prothrombin activation fragment (F1+2), alpha 1 antitripsin (alpha 1 AT), prothrombin time (PT), and activated partial thromboplastin time (PTT). The mean values of PC, PS, and AT III were respectively, 95.7 +/- 16 on HD and 92 +/- 23 on CAPD; 82.2 +/- 13.6 on HD and 90.5 +/- 13.6 on CAPD; the mean value F1+2 was 1.2 +/- 0.5 on HD and 1.04 +/- 0.5 on CAPD (p < 0.05). A good correlation between PS and AT III% functional activity (p < 0.03, r = 0.5) in both groups was found. More-over, PS functional activity was inversely correlated with duration of dialysis (p < 0.05, r = -0.3). HD patients showed a reduction of coagulation inhibitors compared with CAPD patients. Such a phenomenon could justify the increased thrombotic risk in HD patients. Since 80% of those on HD and only 20% of those on CAPD received erythropoietin (EPO), the prothrombotic state in HD could be due to reduced PS activity secondary to EPO treatment.