Work should respect the worker's life and health, leave him free time for rest and leisure, and enable him to serve society and achieve self-fulfillment by developing his personal capacities. This is not what work looks like to hundreds of millions of workers all over the world. Occupational stress arises where discrepancies exist between occupational demands and opportunities on the one hand and the worker's capacities, needs and expectations on the other. III effects are mediated by three classes of mechanisms: (1) feelings of distress (e.g., anxiety, depression, alienation, etc.); (2) behaviors (e.g., increase in alcohol and tobacco consumption, risk taking, self-destructive behavior, etc.); and (3) hyper-, hypo- and dysfunction in various organs and organ systems (e.g., physiological stress reactions as described by Selye; specific changes in endocrine and immunological function, etc.). These effects are common and they are a challenge to occupational medicine. Work environments are man-made and can be adapted by man for man. Local, national and international monitoring of occupational health should be aimed at making work man's servant and not his master.