Erythropoietin (Epo) is an erythropoietic, neurotropic, and angiogenic factor, and may be involved in retinal development. Studies in adult diabetic retinopathy patients reveal significantly elevated vitreal Epo concentrations. It is unknown whether Epo plays a similar role in retinopathy of prematurity. We sought to determine whether Epo is present in the normally developing human eye. Fetal serum and vitreous samples were obtained from 12 to 24 wk gestation. RNA was extracted from isolated retina for Epo mRNA and hypoxia inducible factor-1alpha (HIF) mRNA determination by real-time polymerase chain reaction. Fetal serum was isolated from the umbilical cord. Serum and vitreous samples were analyzed for Epo protein by enzyme-linked immunosorbent serologic assay. In fetal retina, Epo mRNA increased with increasing gestational age, while HIF mRNA remained constant. Epo protein increased with increasing gestation in both vitreous and serum. At each gestational group measured (12-14, 15-17, 18-20, and 21-24 wk), Epo concentrations were significantly greater in vitreous than in serum (p < 0.05). Epo mRNA and protein concentrations increase with increasing gestational age and are greater in the vitreous than serum. We speculate that changes in Epo production following preterm delivery might affect retinal vascular development.