We assessed the clinical efficacy and determined the effective dose of erythropoietin (EPO) in 48 children scheduled for open heart surgery without blood transfusion. The children were divided into three groups: group 1 (n=21) was treated with 300 U/kg of EPO; group 2 (n=11) was treated with 150 U/kg of EPO; and group 3 (n=16) was not treated with EPO. EPO was administered on the day of hospital admission (6 to 7 days prior to surgery), on the following day, immediately after surgery, and on the following day. Immediately after surgery, the hemoglobin concentration in groups 1 and 2 was significantly higher than that in group 3. The reticulocyte count in groups 1 and 2 was significantly higher than that in group 3. Open heart surgery was completed without transfusion in all 21 patients in group 1 (100%), 10 of 11 in group 2 (90.9%), and 11 of 16 in group 3 (68.8%). EPO caused no adverse reactions. In conclusion, EPO was effective as an adjuvant therapy for open heart surgery without blood transfusion in children. Administration of a relatively high dose of EPO (300 U/kg) seems to be effective for pediatric patients.