THE ABSENCE of a prompt physiological response to low blood sugar frequently observed in the human newborn in the initial hours after birth remains an enima.1-4Previous studies have indicated that this hypoglycemic phase is unlikely to be due to functional hyperinsulinism in the normal infant, since intravenous (I.V.) glucose tolerance tests have indicated decreased glucose disposal rates in such infants.5,6However, both glucagon and galactose tolerance tests have suggested that a decreased hepatic response may be the most important determining factor.6,7 The present studies were designed to evaluate whether the newborn puppy would serve as a useful model for studying carbohydrate physiology in the newborn child. Previous studies of other species have demonstrated the variation of enzyme activity,8-11of tissue glycogen content,8,12and of blood glucose with age.10,13The present report compares the physiological responses of normal puppies of varying ages to an