The Japanese have a word for it: Karoshi, or death from overwork. For many of us, our jobs are a major source of stress, and there is a perception that those of us who are lucky enough to have jobs are working harder and harder. This raises the issue of the effects of work on health. When 24-hour blood pressure monitoring first came into use nearly 30 years ago, we observed that for most persons blood pressure tends to be highest during hours of work and that blood pressure tends to be higher on a workday than a day away from work. We also found that the correlation between left ventricular mass and blood pressure was closer for the blood pressure measured at work than for blood pressure taken at home or during sleep. This led us to look at the effects of occupational stress, but the question was how to measure it.