Infants with Rh hemolytic disease can develop a "late" anemia characterized by low serum concentrations of erythropoietin but erythroid progenitors that remain highly erythropoietin-responsive. Erythropoietin administration was evaluated in two patients as an alternative to transfusion. Reticulocyte counts increased after 5 days of treatment, and hematocrits increased after 10 days. Neither patient received erythrocyte transfusions following erythropoietin therapy.