Hemodynamics were evaluated in 8 patients with uncomplicated renal failure on regular dialysis before and after partial correction of anemia by treatment with recombinant human erythropoietin (r-huEPO). Under r-huEPO treatment, mean (+/- SD) hemoglobin increased from 7.51 (0.60) to 10.27 (0.92) g/dl. Mean blood pressure, body weight, total blood volume and extracellular fluid compartment remained unchanged. Cardiac output as measured with a radionuclide method increased significantly from 4622 (1069) to 5393 (1285) units (p less than 0.02) and peripheral resistance decreased from 22 (4) to 19 (3) units (p less than 0.02). 6-keto-1-alpha-prostaglandin decreased from 96.9 (54.4) to 61.6 (18.0) pg/ml (p less than 0.05) but plasma renin activity, noradrenalin and atrial natriuretic peptide remained unchanged comparing pre- and post-treatment levels. This observation suggests that an increase of red blood cell mass can improve heart function in patients undergoing regular dialysis treatment.