Continuous arteriovenous haemofiltration (CAVH) was used in 7 critically ill children: a premature neonate with hypervolaemia secondary to hydrops foetalis and six children aged 9 days to 7 years with acute oliguric renal failure. Biospal 0.5 m2, Renaflo 0.25 m2, Gambro 0.15 m2 and Amicon 0.015 m2 filters were used according to the weights and ages of the patients. Adequate removal of water and solutes was obtained in 6 patients. One of the patients with the smallest filter needed a change to a filter with a larger surface area to improve water and solute removal. Haemofiltration was maintained for between 17 hours and 31 days and was well tolerated. CAVH was discontinued because of recovery of renal function in three patients, improvement of the hypervolaemic state in one, death in three, and transfer to continuous ambulatory peritoneal dialysis because of chronic renal failure in one patient. CAVH is a useful technique for the treatment of acute renal failure and hypervolaemia in critically ill children.