Ten cases of death due to heat stroke are described. They were all young men who collapsed during running exercise or route march and died in hospital later. Post-mortem examination was carried out in all cases. Death was due to disseminated intravascular coagulation with widespread microthrombus formation and coagulative necrosis involving many organs. Meteorological studies showed that at the time of the collapse the environmental temperature was higher than average although it may have been in the morning or evening.