Morbidity and mortality data on myocardial infarction and stroke were collected and analyzed for the Minnesota Heart Health Program areas and mortality data for all of Minnesota, North Dakota, and South Dakota. Computer classification algorithms were developed jointly with the Pawtucket Heart Health Program and the Stanford Five-City Multifactor Risk Reduction Program to allow pooling of data of the three studies. All hospitalized cases of myocardial infarction and stroke were investigated and cause of death was validated for cardiovascular disease deaths occurring out-of-hospital. Deaths occurring throughout Minnesota, North and South Dakota were catalogued. Hospital disease surveillance was carried out with the cooperation of 34 area hospitals. Mortality was ascertained by death certificate counts and from tapes supplied by the three State Health Departments. Morbidity and mortality data were compared between pooled education versus pooled comparison communities and mortality data were compared between these and the remaining areas of the three states.