Continuous venovenous hemodiafiltration (CVVHD) has been increasingly utilized for renal replacement therapy in the critically ill. We report details of a prospective study of CVVHD in 12 critically ill patients (7 males, 5 females; mean age 60 years, range 30-72 years; Apache II score mean 27.4, range 21-35) with oligoanuric acute renal failure supported on CVVHD. Vascular access was obtained via double lumen subclavian or femoral cannulae. The mean pretreatment urea was 35.9 mM/L and the mean pretreatment creatinine was 559 microM/L. After 24 h of treatment on CVVHD these fell to a urea mean of 20.3 mM/L and a creatinine mean of 298 microM/L and remained stable at these values for the duration of CVVHD. The mean net ultrafiltrate volume was 551 mL/h, with a urea clearance mean of 26.6 mL/min and a creatinine clearance mean of 23.7 mL/min. There were no complications related to use of the blood pump module or extracorporeal circuit. Excellent hemodynamic stability, control of fluid and electrolyte balance, and azotaemia control were maintained while on CVVHD. Technique survival was 100%. Patient survival was 42%. We conclude that CVVHD is a safe, effective, and durable therapy for the treatment of acute renal failure in the critically ill and that it offers outstanding metabolic control and cardiovascular stability.