In a comparison of post-dilution haemofiltration (HF) with routine haemodialysis (HD) HF was found to be technically feasible and without difficulty a method of treating end-stage renal failure patients. HF offers the theoretical benefit of a high removal rate of middle molecules at the expense of measured small molecule clearances. The reported improvement in blood pressure and hyperphosphataemia in HF could not be found in our unselected population. The better tolerance to fluid removal during HF may be due to the linear weight loss during treatment but cannot be attributed to constancy in serum osmolality HF (3 X 20-23L ultrafiltrate/week) seems to be an adequate treatment for small patients. In large, heavy patients without significant residual renal function the ultrafiltration volume has to be increased in relation to body weight. HF was found to be superior to HD in patients with fluid removal problems and frequent hypotensive episodes during HD.