Erythropoietin was applied subcutaneously to 49 patients, 41 have been treated by hemodialysis, 3 by continuous ambulatory peritoneal-dialysis, 5 had chronic progressive renal failure. Mean initial dose of erythropoietin was 139.4 U/kg/week and maintenance dose 115.9 U/kg/week. In 43% of patients serum ferritin was decreasing during treatment, and in 20% it was low before the commencing of the treatment. During erythropoietin therapy vitamin B12 was decreasing in 22% of the patients, and the substitution was necessary in 18%. Only in 1 patient it was necessary to substitute also folic acid. There were no nonresponders among erythropoietin treated patients. Elevation of blood pressure was observed in half of the patients, hypertensive encephalopathy in 1, and thrombosis of arterio-venous fistula in 3.