Relationship between blood groups and behavior patterns in men who have had myocardial infarction. Consistent correlations have been found between physical dysfunctional states and blood factors. Some of these disorders have possible psychosomatic components (eg, duodenal ulcer, myocardial infarction). This study focused on the relationship between blood types and various indices of behavior patterns (eg, type A behavior scores, anger ratings) in young patients who had had an initial myocardial infarction. Patients with blood type O scored significantly higher on type A behavior scales and related indices than those having blood type A. Those with blood group B responded on several scales between those with types A and O. We discuss the utility of blood groupings in future research in the prediction of myocardial infarction, methodologic limitations, the relationship of these results to temperament studies, Jenkins Activity Survey subtest patterns, anti-H reactivity pattern, and hypotheses relating blood factors and behavioral traits in patients with psychosomatic disorders. 