In addition to its content of traditional nutrients, milk is a rich source of hormones and peptides, which survive digestion in the neonatal gastrointestinal tract secondary to lower proteolytic activity and increased protein permeability. Previous studies have shown accelerated erythropoiesis or elevated serum erythropoietin (Epo) levels in neonatal (suckling) animals after maternal phlebotomy or maternal hypoxia exposure. We sought to determine whether significant quantities of Epo are present in human milk and whether Epo remains intact under physiologic digestion conditions. Immunoreactive Epo concentrations were determined in 409 human milk samples obtained from mothers of term and premature infants. Samples collected between birth and postpartum d 134 were divided into 11 postpartum day groups. Mean milk-borne Epo concentrations were within the normal range for plasma Epo concentrations and rose with postpartum day (F10,398 = 5.82, p < 0.0001). No differences were observed between milk collected from mothers of premature versus term infants. Estimated weekly human milk-borne Epo intakes approximated the lower range of published parenteral therapeutic doses. In simulated digestion at physiologic pH levels of 3.2, 5.8, and 7.4, milk-borne Epo resisted degradation at 1 and 2 h, compared with baseline. Therefore, we conclude that human milk contains considerable amounts of Epo which resist degradation after exposure to gastric juices at physiologic pH levels. These results support continued investigation into the fate and developmental roles of Epo in human milk.