Small, conditioned dogs underwent deep hypothermia by peritoneal dialysis, followed by a 30-minute circulatory arrest and rewarming. Direct cooling of the viscera induces hypothermia more rapidly than topical hypothermia. All animals survived with no neurologic deficit. Respiratory alkalosis was induced by constant ventilation with room air as nasopharyngeal temperature declined. Ventricular fibrillation did not occur unless the ventricles were manipulated. Histologic studies indicated no damage to heart, lung, kidney, liver, or jejunum. This technique may be applicable to cardiac surgery in infants.