Twelve patients with renal failure and type A lactic acidosis were treated with haemofiltration during a 30-month period. The first three patients received only lactate-buffered replacement fluid and rapidly succumbed despite the infusion of large quantities of sodium bicarbonate. Bicarbonate-buffered replacement fluid was used for the remaining nine patients, of whom three survived. Haemofiltration with bicarbonate-buffered replacement fluid is an effective method of replacing renal function for this group of critically-ill patients.