Regular haemodialysis with the Kiil dialyser for 8-10 h three times a week is the present standard of adequate dialysis. In 100 patients treated by this regime there was no positive correlation between plasma urea and creatinine before or after dialysis and any of the symptoms of which these patients still complained. There are no grounds for believing that a further increase in dialysis would relieve residual symptoms. However, any reduction in current standards of dialysis should be justified by prolonged clinical trial of large groups of patients before they are accepted as equivalent in view of the infrequency of some uraemic manifestations such as pericarditis. The implications of the middle molecular hypothesis are discussed.