The biochemistry of human life depends on a stable core temperature of 98.6F and remains at peak efficiency only within a few tenths of a degree variation. Significant pathology is associated with temperatures that are either above or below the normal range of 98.3-98.9F. In this presentation, Dr. Nesbit addresses a brief overview of the evolution of thermoregulation and then discusses the etiology of a few of the diseases associated with low body temperature.