The mortality of patients with combined acute hepatic and renal failure remains high. Previous studies have reported both patient morbidity and mortality directly attributable to the use of extracorporeal circuits used to treat renal failure. We investigated the effect of various modes of renal replacement therapy in 30 consecutive patients referred with both fulminant hepatic and acute renal failure. Cardiac output decreased during the first hour of 30 intermittent machine haemofiltration treatments, by 15 +/- 3%, as did tissue oxygen delivery, 16 +/- 3% and tissue oxygen uptake, 13 +/- 4%, whereas there was no significant change during 30 continuous hemofiltration and/or dialysis treatments. Intracranial pressure remained stable during the continuous modes but increased from 9 +/- 2 mm Hg to 17 +/- 2 mm Hg, P < 0.01, during intermittent machine hemofiltration, with the greatest increase of 55 +/- 9% within the first hour. Mean arterial blood pressure was stable during treatment with the continuous modes, but decreased by 20 +/- 3% during the first hour of intermittent machine hemofiltration, resulting in a maximum reduction in cerebral perfusion pressure of 35 +/- 8%. In this group of critically ill patients continuous modes of renal replacement therapy resulted in superior cardiac and intracranial stability compared to standard intermittent modes of treatment.