Eighteen patients aged 5-18 years on regular dialysis had a packed cell volume (PCV) less than 0.27. On treatment with epoetin alfa (EA) PCV increased by 0.05 or more in all patients. Iron supplementation was necessary in 13 patients with a ferritinaemia less than 300 micrograms/l before study. During treatment, plasma potassium increased significantly and more vigorous antihypertensive measures were required in 8 patients, 5 of them being already on antihypertensive drugs before EA. Iliofemoral thrombosis occurred in 1 patient 10 days after renal transplant. The data indicate that EA ameliorates the anaemia of chronic renal disease. The main concerns arising during treatment with EA are hyperkalaemia, arterial hypertension and possibly thrombosis.