Glucose metabolism and changes in plasma insulin, glucagon and catecholamines were studied in unfed newborn pigs during acute cold exposure immediately after birth. When newborn pigs are exposed to a moderate cold external temperature (20 degrees C), they exhibit a transient thermoregulatory response characterized by an increased liver glycogenolysis, an enhanced blood glucose clearance rate (+35%) and a rise in plasma catecholamine concentrations. When the newborn pigs are exposed to a cold external temperature (12 degrees C), they become rapidly (10-12 h after birth) hypothermic and hyperglycaemic. This results from a fall in blood glucose clearance rate (-40%). Muscle glycogenolysis is low in normothermic animals during the 12 h following birth. Muscle glycogenolysis increases after a delay of 6 h in animals exposed to an external temperature of 20 degrees C or 12 degrees C. These data demonstrate that the failure in the thermoregulatory response in the newborn pig exposed to a cold temperature is not the consequence of a lack of mobilization of energy stores, but results from a defect in glucose utilization.