Psychosocial work characteristics, such as work demand, work control, and social support at work, have been shown to be related to the development of coronary heart disease in epidemiological studies. However, the mechanisms which mediate the social and psychological effects on the cardiovascular system are not known. We have studied the direct cardiovascular effects of psychosocial work environment characteristics in 148 working men and women, representing seven different occupational groups (physicians, teachers, musicians, policemen, train engineers, prison personnel, and saw mill workers). Besides standardized measures of work demand, work control, and social support, ambulatory 24-hour monitoring of electrocardiograms in the customary work and home environment was performed. Systolic and diastolic blood pressure were measured as well as other standard physiologic risk factors for coronary heart disease. Mean heart rates were found to be significantly higher in persons reporting low social support at work. This effect was maintained during working hours as well as during leisure time and rest. Of the other related physiologic risk factors, systolic, but not diastolic blood pressure was found to be higher in persons reporting low social support. Smoking, alcohol consumption and relative body mass index were not related to social support at work. Controlling for age, sex and physical strain at work, strengthened the association of low social support with elevated heart rates.