Erythropoietin (Epo) synthesis within the central nervous system (CNS) has been shown to be developmentally regulated and responsive to hypoxic stimuli in the murine model. Functional Epo receptors within the developing CNS have also been documented in this animal model. As recombinant (r)Epo is gaining acceptance as a therapeutic modality for the treatment of anemia of prematurity, we sought to determine whether Epo is present within the CNS of developing humans, and whether treatment of premature infants with rEpo affects these levels. Our objectives were to: 1) determine whether Epo is present in the cerebrospinal fluid (CSF) of preterm human infants, 2) determine whether CSF Epo levels are affected by prenatal or postnatal age, and 3) determine whether Epo concentrations in preterm spinal fluids are influenced by treatment with rEpo. Epo was quantified by specific ELISA in 55 CSF samples. Thirty samples were from preterm and term neonates. Fifteen of these patients were being treated with rEpo for anemia of prematurity. Epo was present in the CSF of all neonates tested. Patients treated with rEpo trended towards higher CSF Epo concentrations 13.1 ± 12.9 mU/mL (range 4.0 mU/mL to 51.4 mU/mL) vs 9.2 ± 7.5 mU/mL (range 2.3 mU/mL to 21 mU/mL), p=0.06. To assess the effect of age on CSF Epo concentrations, 25 CSF samples from individuals ranging in age from 1 month to 33 years were assayed for the presence of Epo. During infancy, the mean CSF Epo concentration was 5.2± 9.3 mU/mL, with a median concentration of 2 mU/mL, and a range from 0 to 32 mU/mL. All individuals greater than 3 months of age had levels of less than 4 mU/mL, with the mean and median concentrations being 2.0 ± 4.8 mU/mL and 0 mU/mL, respectively. We conclude that Epo is present within the CSF of preterm and term infants, that it probably increases with rEpo treatment, and that it appears to be developmentally regulated.