Systemic glucose production rates were measured in 6 normal newborn infants by dilution of glucose-1-13C tracer according to the prime constant-rate infusion technique. Glucose production rates were 4.4 +/- 0.39 mg/kg. min. (Mean +/- S.D.) in 4 infants at 2 hours of age, and were 3.83 and 3.86 mg/kg. min. in 2 infants at 1 day of age. Systemic glucose production accounts for 50% of the substrate utilized for oxidative metabolism in newborn infants.