This study was performed to determine the effect of recombinant human erythropoietin (rEPO) on preoperative autologous blood donation in patients undergoing elective coronary bypass or valvular operations. Nineteen patients received 200 u/kg of rEPO intravenously 3 times a week, and 210 mg/day of iron sulfate orally, for 2 weeks before surgery (EPO group). Seven matched patients only took the same dose of iron sulfate (control group). Bone marrow was aspirated from the sternum during surgery, and the Myeloids/Erythroids ratio was calculated in 13 patients of the EPO group. The total donated blood mass was 853 +/- 231 g in the EPO group, and 657 +/- 140 g in the control group (p < 0.05). The average increase in hemoglobin (Hb) mass from admission to the day before surgery was 87 +/- 33 g in the EPO group, and 24 +/- 13 g in the control group (p < 0.001). Furthermore, the logarithm of the ratio of "increased Hb mass/Hb mass at admission" was significantly correlated to the Myeloids/Erythroids ratio (r = -0.9130, p < 0.01). These results strongly indicate that rEPO is a very useful agent for predonation of autologous blood for cardiac operations.