Beagle bitches, obtained 3 weeks post-conception, were fed one of two diets; diet 1 contained 44% of metabolizable energy from carbohydrate and diet 2 contained 0% of metabolizable energy from carbohydrate. Bitches consumed similar amounts of energy from the two diets. Plasma glucose levels were similar in bitches fed the two diets, except in the week before whelping. At this time, plasma glucose levels as low as 15--20 mg/dl were observed in several bitches fed diet 2. None of the bitches fed diet 1 exhibited hypoglycemia. Bitches fed diet 2 also had depressed plasma levels of alanine and lactate and elevated levels of free fatty acids and B-hydroxybutyrate near the end of gestation. Total number of pups whelped by the bitches was unaffected by diet, but fewer pups from bitches fed diet 2 were alive at birth (63%) than from bitches fed diet 1 (96%). Only 35% of the pups whelped by bitches fed diet 2 were alive at 3 days of age. Milk from bitches fed diet 2 had a lower percentage of energy from lactose and a higher percentage of energy from fat than did milk of bitches fed diet 1. Growth of pups, however, was unaffected by composition of diet fed to the bitches. We concluded that pregnant bitches require dietary carbohydrate for optimal reproductive performance.