The association between physical activity at work and at leisure, coronary risk factors, social class and mortality has been studied in about 15000 Oslo men, aged 40-49, without known cardiovascular disease or diabetes at a screening examination for coronary risk factors. Four-year total and CHD mortality showed a decrease with increasing degree of leisure activity, and an increase with increasing work activity. The three conventional coronary risk factors--serum cholesterol, systolic blood pressure (SBP) and number of cigarettes--associated negatively with physical leisure activity, whereas they all associated positively with physical activity at work. Men in lower social classes were less active at leisure but more active at work than men in the higher classes. In a multivariate analysis of variance with coronary risk score (based on SBP, serum total cholesterol and number of cigarettes), social class and physical activity, the predictive power of physical leisure activity for future death was almost as good as the coronary risk score. Physical activity at work, on the other hand, was not an independent risk factor either for total or for CHD mortality.