Hypertension and atherosclerotic cardiovascular disease have been ascribed to a variety of host-environmental characteristics -- cigarette smoking, modern-day dietary practices, abnormal blood lipid and blood glucose patterns, obesity, psychosocial factors, genetics, etc. -- together with the decline in vigorous job activity because of mechanization and related developments in industry and transportation. To the extent that job assignments limit exercise opportunities, leisure-time physical activity may be of increasing importance in the control and reduction of coronary heart disease. There is need to determine what levels, frequencies, and intensities of exercise exist in modern American lifestyles--particularly the trends of exercise enthusiasm, and how these have changed during the periods of increasing and decreasing cardiovascular incidence from 1912-1967 and 1968 to date, respectively. There is need to know what physical demands on the human body are essential to maintain cardiac and vascular well-being in successive age groups, including old age, and what conversion from a sedentary to an active lifestyle can mean to the betterment or detriment of man's health. The present study began as an intramural project of the National Heart Institute in 1961 and has continued to date, becoming an extramural project in 1968. Approval was received from the NIH and the universities concerned to use the baseline data collected from college physical examinations, social and athletic records of male students examined at Harvard University between 1916-1950 and at the University of Pennsylvania between 1931-1940.