From November 1976 to September 1978, a total of 3,179 active men, 40-55 years old, were screened for established or possible risk factors. Standard questionnaires were administered to assess psycho-social behavior and physical activity on and off the job. Physical fitness was determined by means of a graded sub-maximal exercise test. Information on coronary heart disease incidence will be collected over a 6-year period. The main objective of the study is to establish prospectively if physical activity and/or physical capacity are independent risk factors. Intercorrelations between fitness, physical activity and other measured variables will be analyzed. Doppler ultrasound and 24-hour ECG recording for detecting peripheral vascular disease and rhythm disturbances have also been used; their value and role in screening for cardiovascular disease is further discussed.