COLORADO has been among the first five states in deaths from rheumatic heart disease among school children for twenty years.1 A preliminary examination of 1,845 Denver school children revealed a prevalence of 1.6 per cent, which is not unusual when compared with that of other areas.2 One report has appeared suggesting that the prevalence of rheumatic heart disease increases with increasing altitudes.3 Chavez reported that there is a higher incidence of rheumatic heart disease among adults who die of heart disease in México, D. F., Mexico, where the altitude is 8,000 feet (2,438 meters), than anywhere else in the world.4 The altitude in Denver is 5,183 feet (1,580 meters), but the altitude in Colorado ranges from 3,350 to 14,431 feet (1,021 to 4,399 meters), with an approximate mean of 6,800 feet (2,073 meters). It seemed possible that the high death rate among children in Colorado might