In order to clarify the influence of membrane surface, membrane composition, dialysate buffer and convective transfer on the dialytic removal of inorganic phosphate (Pi), 11 uremic patients were studied. Each patient underwent 7 different dialysis techniques: conventional hemodialysis with acetate buffer and different surface or composition of the membrane, bicarbonate dialysis and a "soft" hemodiafiltration, also termed biofiltration, with post-dilution infusion of 4 liters. The treatment time was fixed at 4 hours. Our study showed that the dialyzer surface area and the ultrafiltration rate were the major factors in dialytic inorganic phosphorus (Pi) removal. The dialysate buffer does not modify dialytic Pi removal but may influence the rebound phenomenon.