Although it is now firmly established that coronary heart disease mortality rates in the United States have fallen by about 50 percent since the mid 1960's, there has been no systematic program to study in parallel coronary heart disease morbidity and the prevalence of atherosclerosis. Such information is essential for an understanding of the factors influencing the time trends, for quantifying the effects of prevention versus treatment, and for guiding future policy in research and services. It remains a possibility that the mortality decline in past years was not accompanied by a reduction in incidence, or a diminution in the extent of the underlying arterial diseases. A trend confined to mortality would require different explanations and call for different strategies of prevention than a decline encompassing the whole spectrum of clinical manifestations, which would favor a risk factor explanation. ARIC surveillance provides cardiovascular incidence rates, and its cohorts provide information on atherosclerosis, cardiovascular symptoms, new and established risk factors and medical care utilization on representative residents of each community. New predictors of both atherosclerosis and cardiovascular diseases are investigated using data obtained at four examination centers, the ultrasound center and five central laboratories.