A substantial reduction of body temperature has been employed by several investigators in recent years as a useful therapeutic procedure. It was devised by Smith and Fay1 originally for the treatment of patients with metastatic malignant growths and has been extended subsequently to the treatment of patients with other conditions.2 The depression in the internal body temperature which may be produced by the general application of cold to the subject's skin belies common opinion concerning the minimum critical temperature. Internal body temperatures which range from 80 to 90 F. may be maintained continuously, if due precautions are exercised, for as long as seven days. After such a treatment the patient appears to have suffered no undesirable effects. Smith and Fay chose hibernation as a fitting term for the treatment, while others have called it refrigeration, freezing, frozen sleep and crymotherapy. It is believed that a valid criticism may