Comparative studies were performed on 19 patients who were dialysed initially for a mean of 25 h a week and then for a mean of 11.1 ha week over two 3-year periods. Clinical, biochemical, haematological and neurological valuations were performed, which showed no significant difference. As an adjunct to haemodialysis a perfusion system was added to 12 of these patients already stable on haemodialysis and estimations made of removal of middle molecular weight substances from plasma by a gel filtration method through a Sephadex column. The results of these various techniques are reported and the comparisons between haemodialysis, haemodialysis and ultrafiltration and haemodialysis, perfusion and ultrafiltration are given.