Rewarming from immersion hypothermia has been assessed in sheep by the use of three techniques--hot bath, body insulation and airway warming. Though the hot bath was the fastest of the methods of rewarming studied, consideration of temperature gradients and therefore total body heat diminished its advantage in comparison with central body rewarming via the airway (CBRW), which in turn showed considerably advantage over body insulation alone. CBRW did not have any thermal advantage gained on assisting the ventilation as compared with spontaneous breathing. The results illustrate the importance of adequate insulation of the body to prevent further heat loss and this was found to be true whether or not airway warming was being used. The site of heat uptake with CBRW was determined and observations were made on the physical behaviour of temperature gradients.