We describe our preliminary experience with five children who received acetate-free biofiltration, a modification of haemodiafiltration without buffer in the dialysate and simultaneous infusion of bicarbonate through a venous port. Adequacy of haemodialysis (HD) was achieved with 3 h treatments three times per week (mean Kt/v 1.35 +/- 0.29, mean protein catabolic rate (PCR) 1.4 +/- 0.3 mg/dl). During the session, pH increased from 7.4 pre HD to 7.5 post HD. The mean bicarbonate infused as a 0.166 M solution averaged 235 +/- 35 mEq/h. Hypertension did not occur. There were no cramps, hypotension or vomiting. Bicarbonate requirements correlated significantly with dialyser surface area and body weight (r = 0.76, P < 0.001).