Shivering appears to be directly related to the central nervous system temperature rather than to peripheral body temperature. Selective heating of the brain stem produces panting. Re-warming of the body is retarded by initiation of heat loss mechanisms controlled centrally when hyperthermic perfusion is employed. Shivering disappears with pentobarbital sodium anesthesia, whereas panting is not affected. Cooling of the cerebral cortex (1 or both of the frontal areas) and the anterior part of the 3rd ventricle does not significantly affect the respiratory or circulatory systems. Brain stem hypothermia produces distinct respiratory and circulatory reaction. Cooling of the 3rd and 4th ventricular areas may be utilized for anesthetic purposes.