The first Whitehall Study of British civil servants demonstrated an inverse gradient in mortality. The lower the grade the higher was the mortality risk. This higher mortality risk applies to most but not all causes of death. The Whitehall II Study, set up to investigate causes of this social gradient shows similarly marked gradients in morbidity. A review of potential causes of the gradient suggests that it is due neither to health selection nor simply to differences in lifestyle, but that relative deprivation-a psychosocial concept-and the accumulation of socially-patterned exposures over the life course, must be important. Whitehall II suggests that the operation of these factors is to be found in the specific circumstances under which people grow, live and work.