Atherosclerosis Risk in Communities (ARIC) is a new prospective study to investigate the etiology of atherosclerosis and its clinical sequelae and variation in cardiovascular risk factors, medical care, and disease by race, sex, place, and time. In each of four US communities--Forsyth County, North Carolina, Jackson, Mississippi, suburbs of Minneapolis, Minnesota, and Washington County, Maryland--4,000 adults aged 45-64 years will be examined twice, three years apart. ARIC has coordinating, ultrasound, pulmonary, and electrocardiographic centers and three central laboratories. Three cohorts represent the ethnic mix of their communities; the Jackson cohort, its black population. Examinations include ultrasound scanning of carotid and popliteal arteries; lipids, lipoproteins, and apolipoproteins assayed in the Lipid Laboratory; and coagulation, inhibition, and platelet and fibrinolytic activity assayed in the Hemostasis Laboratory. Surveillance for coronary heart disease will involve review of hospitalizations and deaths among community residents aged 35-74 years. ARIC aims to study atherosclerosis by direct observation of the disease and by use of modern biochemistry.