This application from the University of Pennsylvania School of Medicine and the Children's Hospital of Philadelphia is to participate with the NICHD under a cooperative agreement in an ongoing multicenter Neonatal Research Network (NRN) designed to perform interventional and observational clinical studies in newborn infants, particularly low birth weight infants. The objective of this program is to facilitate the advancement of neonatal care by establishing a network of academic centers that, by rigorous patient evaluation using common protocols, can study the required numbers of patients and can provide answers more rapidly than individual centers acting alone.