We studied 7 patients on chronic hemodialysis before and after 12 weeks of therapy with human recombinant erythropoietin. The drug was administered intravenously, 3 times a week at doses increasing from 50 to 125 U/kg. Dialysis was performed for 4 hr, 3 times a week and no blood transfusions were used during the study. An increased tolerance to daily physical activities was observed in all patients. Hematocrit increased from 19 +/- 3.4 to 28 +/- 4.1 and hemoglobin from 6.7 +/- 1.3 to 9.4 +/- 1.5, p less than 0.01. No changes were detected in blood pressure, weight, liver function tests and nutritional values. No patient developed either absolute (ferritin less than 30 ng/ml) or relative iron deficiency (transferrin saturation less than 20%) during the study. Efficiency of dialysis remained unaltered. No secondary effects from the drug were observed. Thus, this study confirms the clinical usefulness of human recombinant erythropoietin in patients with chronic renal failure and anemia on chronic dialysis.