Erythropoietin (EPO) is a glycoprotein hormone and the principal regulator of erythropoiesis in the fetus, newborn, and adult. EPO-alfa is erythropoietin manufactured by recombinant human DNA technology (rhEPO). After counseling, a pregnant woman with anti-Js(b) in her serum was started on rhEPO (600 U/Kg, biweekly) to prevent anemia secondary to serial donations of her blood for fetal transfusions. After a total of 25 rhEPO infusions and autologous donation of 8 units of whole blood, maternal hemoglobin prior to the elective cesarean section at 37 weeks was 11.3 gm/dL. Serum EPO concentration was determined in paired maternal and fetal blood samples, before ultrasound guided intravascular transfusions, in this alloimmunized Js(b)-negative and another Rh(D) alloimmunized pregnancy to determine possible correlations between maternal and fetal serum EPO. rhEPO prevented anemia in a patient who donated 8 units of blood from 18-37 weeks of pregnancy without inducing adverse biological effects such as hypertension or thrombotic complications in the placenta. Data presented in this study suggest that EPO does not cross the human placenta.