Much of the medical and epidemiological research on the causes of cardiovascular disease has concentrated either on individual life style behaviors such as smoking and exercise or on biomedical risk factors such as hypertension, and diabetes. This research has provided the basis for improvements in personal health behaviors and in the treatment of hypertension which has reduced the incidence of cardiovascular disease in this country. However, even the best statistical models, incorporating all such risk factors, leave a significant proportion of cardiovascular disease mortality and morbidity unexplained. Major differences in cardiovascular disease rates have also been observed between different social classes and different societies. These findings have led epidemiologists and sociomedical researchers to investigate other types of variables, including psychosocial factors, such as personal predispositions, social support networks, and work-related stress. A series of studies, in a variety of disciplines, suggested that occupational stress may contribute to the development of cardiovascular disease.