The purpose of this study is to investigate in a quantitative and qualitative manner the nature of energy metabolism in the neonate. A subhuman primate model (the neonatal and infant baboon) has been used for quantitative investigations of energy metabolism. Utilizing appropriately placed arterial and venous catheters for sampling of arteriovenous metabolite differences and the radioactive microsphere technique for measuring organ blood flow, cerebral, hepatic, renal, and muscle substrate uptake and production as well as oxygen consumption and carbon dioxide production are in the process of being evaluated. In addition, clinical studies are being conducted utilizing measurements of arterial and venous substrate levels in high risk infants and infants with hypoglycemia or hyperglycemia. Correlations with clinical condition are being made. BIBLIOGRAPHIC REFERENCES: Levitsky, L.L., Paton, J.B., Fisher D.E. and DeLannoy, C.W.: Uptake of glucose and release of gluconeogenic precursors by the hindlimb of the fasting baboon neonate. Accepted for presentation, Soc. Pediatr. Res., 1977.