Cloning and expression of the human gene encoding erythropoietin has resulted in the availability of recombinant erythropoietin for clinical and laboratory investigation. Results of such investigations are clarifying the mechanisms that regulate production of erythropoietin in health and disease. It seems likely that erythropoietin administration will reduce, if not replace, erythrocyte transfusions for certain pediatric patients. Those with the anemia of end-state renal disease and anemia of prematurity may be most likely to benefit. Clearly, additional well-controlled studies to assess the risks and benefits of erythropoietin administration will be needed prior to widespread usage of erythropoietin for anemic children.