An alternative title to my paper might be "pathology of inactivity" or, even, "occupational hazards of sedentary and light work." Technical development has involved a drastic reduction of physical activity in work, in transportation, and probably in leisure too. Indications are that this trend will continue and increase. Up to now, most investigations of it as a health problem have related to activity and inactivity of jobs. Some current epidemiologic studies in the Social Medicine Research Unit of the British Medical Research Council will be reported.1 Coronary Heart Disease in London Busmen Studies of coronary heart disease among London busmen begun in 1949 showed almost at once that the drivers suffered more commonly from sudden death due to coronary heart disease than the conductors (ticket collectors) of these double-decker vehicles.2 Data have now accumulated for 10 years (Table 1). This shows that, under 50 years of age, drivers