We conducted a prospective observational study to assess the efficacy of continuous venovenous hemofiltration (CVVH) with no anticoagulation. A standard anticoagulation protocol for CVVH, which prescribed no anticoagulation for patients at risk of bleeding, was applied to 48 critically ill patients treated with CVVH. Circuit life was prospectively observed, and the following data were obtained for each circuit: heparin use and dose, protamine use, daily prothrombin time-international normalized ratio, activated partial thromboplastin time, and platelet count. Out of 300 consecutive circuits, 143 (47.6%) received no anticoagulation, 31 (10.3%) received regional anticoagulation, and 126 received low dose heparin. No patients experienced bleeding complications secondary to CVVH. Platelet count was significantly lower in the no anticoagulation group (73 x 10(3)/microl) compared with the low dose heparin group (119 x 10(3)/microl) and the protamine group (104 x 10(3)/microl) (p < 0.01 for both comparisons). There was no significant difference in mean circuit life among the three groups (heparin, 20.9 hours; no anticoagulation, 19.3 hours; protamine, 21.2 hours; not significant). In conclusion, for a group of patients deemed to be at risk of bleeding, CVVH without anticoagulation achieved an acceptable circuit life, which was similar to that obtained in other patients with low dose heparin anticoagulation or regional anticoagulation with heparin/protamine.