We have demonstrated in experiments on chickens and swine that the behavioral repertoire of a species and social structure of its environment are major factors in the rates of progress of arteriosclerotic stenosis of intramural coronary arteries and possibly of cerebrovascular lesions. Current objectives are to relate behavioral responses of two species with dissimilar behavior patterns in corresponding social situations to biochemical and pathological changes, especially cardiovascular and cerebrovascular changes. This will involve studies on blood pressure, steroid blood levels and catecholamine excretion as well as appropriate postmortem studies.