Since 1973 haemodialysis was performed on 30 children with severe haemolytic-uraemic syndrome. Serial measurements were made of blood pressure, blood picture, renal function, complement values, excretion of fibrinogen split-products and beta2-microglobulin in urine. Of 22 children in the acute severe stage two died, in one case treatment having been started too late, in the other as a result of fulminating pneumococcal pneumonia. Twenty children survived without residual symptoms and with normal renal function. Of six children with severe progressive haemolytic-uraemic syndrome two developed terminal renal failure. In one child a renal transplantation has since been performed. One child requires chronic dialysis after nephrectomy. Three children died as a result of arterial hypertension, one of yeast septicaemia. Of two children with recurrent haemolytic-uraemic syndrome one developed terminal renal failure which was successfully treated by renal transplantation. One child died in a hypertensive crisis. The overall death rate of the group was 23%, in the group with the acute severe haemolytic-uraemic syndrome it was 9%. The results suggest that haemodialysis significantly improves the prognosis of severe haemolytic-uraemic syndrome.