Thirty patients with end-stage renal disease were switched from maintenance hemodialysis to postdilution hemofiltration and observed for long-term effects. The study comprised totally 496 months of hemofiltration. Uremic and biochemical control was similar in the hemofiltration and in the hemodialysis period. Of the small molecules, only serum creatinine showed slight increase after 3 months. No other significant changes in creatinine, serum urea or potassium levels were associated with long-term hemofiltration. During each hemofiltration session there was significant decrease of serum parathyroid hormone (PTH) and serum beta 2-microglobulin, but over the first 8 months of hemofiltration the beta 2-microglobulin values did not fall, and significant PTH reduction was found only after 12 months. Although uremic control was similar with both methods, there were fewer complications of hemofiltration, which was preferred by the patients. Because it is currently more expensive, however, hemofiltration should be reserved for patients with dialysis related problems, that are not helped by other changes in the dialysis technique, such as sequential ultrafiltration changes in the dialysis membranes and in the dialysis buffer from acetate to bicarbonate.