The pharmacokinetics and pharmacodynamics of enoxaparin were studied in healthy volunteers and hemodialysis and peritoneal dialysis subjects. Antifactor Xa activity estimated the pharmacokinetics, whereas thrombin generation time (TGT) estimated the pharmacodynamics. Enoxaparin 1 mg/kg was given subcutaneously to all subjects. Antifactor Xa Amax and AUC0-12 were similar between groups, but the TGTmax was significantly greater in the dialysis groups (P =.001). The thrombin generation time remained significantly more prolonged throughout the 12-hour study period, and there was a trend toward greater TGT AUEC0-12 for both dialysis groups [P =.07). Patients receiving hemodialysis had greater sensitivity to enoxaparin compared to the other groups. These results suggest that in dialysis patients, there may be accumulation of active heparin metabolites that are undetected by the antifactor Xa assay. Therefore, these subjects exhibit greater thrombin generation time prolongation despite similar antifactor Xa exposure. Further largescale studies are needed to corroborate the results of this exploratory pilot study.