A previous study in a car assembly plant showed that production-line workers had a lower incidence rate of heart attacks than executive staff. In the present study some major coronary risk factors and 24-hour ambulatory electrocardiograms were investigated in two age-matched samples of 30 middle-aged men drawn from these occupations. Men with a known history of heart disease were excluded. Compared with production-line workers, executive staff on average had a higher diastolic blood pressure (P less than 0.05) and fewer took heavy exercise during their leisure time (P less than 0.05). Ventricular premature beats (VPB was also similar for each of the periods of work, leisure and sleep. Apart from isolated ectopic beats, disturbances of rhythm were uncommon, and neither VPB nor other arrhythmias appeared to be induced by occupational factors.