In the British civil service studies, as in the country as a whole, social class is defined on the basis of occupation. This raises the question as to whether the observed differences in morbidity and mortality are due to factors related to occupation or the general way of life. In many countries there are well documented social class differences in aspects of life-style: smoking, leisure-time physical activity, obesity, diet. Such differences were confirmed in civil servants studies, but these were insufficient to account for differences in mortality. There are thus two types of question: what accounts for the differences in smoking and other aspects of life style among men and women in different occupations? and; to what extent may the unexplained social differences in disease rates be related to factors associated with work as distinct from way of life?