We measured the intracranial pressure (ICP), using a subdural catheter in nine patients admitted with grade 4 hepatic encephalopathy due to fulminant hepatic failure complicated by oliguric renal failure. Six patients received daily machine haemofiltration and four patients were treated with continuous arteriovenous haemofiltration (CAVHF). The mean ICP increased during the first hour of machine haemofiltration from 9 ±1.4 mmHg to 13 ±1.8 mmHg (P<0.05), and there was a reduction in the mean arterial pressure from 92.4 ±2.7 mmHg to 81 ±3.2 mmHg (P<0.05) resulting in a reduction in cerebral perfusion pressure of up to 30%. The group treated by CAVHF, although having a greater mean ICP prior to treatment (19 ±4.8 mmHg) and a lower mean arterial pressure (66 ±3.6 mmHg) and consequently a lower cerebral perfusion pressure, did not show any increase in ICP or reduction in mean arterial or cerebral perfusion pressure. There was a significant reduction in serum osmolality during the first hour of treatment in the machine haemofiltration group (314 ±4 mOsm/kg to 309 ±4 mOsm/kg, (P<0.05), whereas there was no corresponding change in the CAVHF group. This suggests that CAVHF is to be preferred for the treatment of acute renal failure in such patients who are at considerable risk of developing cerebral oedema. © 1990 European Dialysis and Transplant Association-European Renal Association.