During the month of July, 1942, admissions due to heat disability reached a rate of 15.5 per thousand per annum, a significant loss of manpower. Even with our appreciation of the importance of preventive measures, greater knowledge of mechanisms involved, and regulations, in effect, prohibiting thermal injuries, there were close to 300 admissions to hospitals for heat disability in the armed forces in 1952. Heat disability falls into three categories: heat cramps, heat exhaustion, and heat stroke. Sunstroke, a diagnosis used by some, should be considered as heat stroke, and not as a separate entity. The physical regulation of body temperature consists of several mechanisms. The most important are radiation, convection, and conduction, accounting for 65% of heat loss; evaporation of water from the skin and lungs, accounting for 30% of heat loss, and two relatively unimportant mechanisms, heat loss from raising temperature of inspired air, and heat lost in