Heat illness prevention activities began in Missouri in the summer of 1980 with investigation of heat wave related deaths in St. Louis and Kansas City. Findings from these studies were used to develop a statewide heat illness prevention program. The St. Louis metropolitan area developed an "Operation Weather Survival" with cooperation of multiple public and private agencies. The Steadman Apparent Temperature Index has been used for state purposes while the St. Louis area relied for many years on the Wet Bulb Globe Temperature for decision making. Trends of heat related morbidity and mortality will be presented. Revisions in the terminology used for public notification have recently changed to parallel more closely the Weather Service "watch/warning" system.