As part of the Swiss National Research Program for the Prevention of Cardiovascular Disease, the degree of physical activity at work and during leisure time ws investigated in 3614 men and 4221 women living in four Swiss cities. Some 50% of the men and more than 60% of the women were considered insufficiently active. Since their jobs involve little physical activity, the quantity and quality of exercise needed for prevention of coronary heart disease can only be obtained from sports during leisure time. Of the men and women investigated in Aarau, 65 and 61% respectively volunteered for a bicycle ergometer test while in Nyon the participation in this part of the study was considerably lower (29 and 24% of the men and women). In both sexes and all age groups the mean values for the extrapolated maximum oxygen uptake were comparable to those reported from other highly industrialized countries.