All infants previously enrolled in NCT00334737, a randomized masked study of darbepoetin administration in preterm infants, are eligible for the study. We anticipate enrolling 75 of the original 102 infants from that study. In addition we will enroll 25 preterm infants who did not receive Epo treatment during hospitalization, and 36 term infants matched for age, gender and ethnicity to the preterm group.