Eleven hypothermic patients were treated by heat supplied via the airway. Three patients died during rewarming, three died of unrelated causes several days after successful rewarming and five survived. Core temperatures were measured by a low reading mercury rectal thermometer and by a thermistor probe inserted into the rectum or mid-oesophagus. In every patient the core temperature rose without any initial after-drop. The problems of the method are discussed and the suggestion made that it might be applicable in rescue work, in the treatment of elderly hypothermic patients, and in combating accidental hypothermia in the operating theatre.