SummaryHypothermia is not a therapeutic measure per se–it merely lowers metabolism and permits the vital organs to withstand prolonged hypoxia. Therefore, the prime indication for therapeutic hypothermia must be reversible hypoxia of vital organs.At present the greatest application is in disorders of the central nervous svstem. To be effective the temperature must be lowered to a point where metabolism is appreciably diminished. The highest useful temperature for central nervous system disorders is 30%C and probably much lower temperatures are more effective, especially if a major bloodsupply to a portion of the brain or spinal cord is to be interrupted.In cases of hyperthermia and in acute infections it is probably not necessary to coolbelow 3244%C.The technique involves surface cooling with sedation to control restlessness and shivering; so far chlorpromazine appears to be the best agent for this purpose. Initial hypertension is controlled by vegolysen.The procedure does not appear to be particularly hazardous provided detailed precautions are observed. The chief danger is ventricular fibrillation which is not a common complication in this type of patient who usually has a normal cardiovascular and respiratory system.There is much conflicting experimental evidence on the metabolic effects of prolonged hypothermia.It is important that we determine in human beings the significance of these alterations in metabolism and particularly whether these changes are normal physiological phenomena for the lower temperatures. It must also be ascertained whether the complex changes associated with hypothermia can be reversed after prolonged periods of low temperatures.With greater knowledge of the physiology, better sedatives and drugs to control shivering and more careful monitoring of the patient, we should be able to achieve even lower temperatures.There is every indication that, under these conditions, hypothermia will have a definite place as an adjunct to modern therap