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The blood pressure and heart rates of seven normotensive shift workers were monitored automatically for 24 h with a non-invasive ambulatory method on 3 different days. The first monitoring session took place at the end of an ordinary work period of morning shifts, the second on the first day of a period of night shifts, and the third on the last day of a period of night shifts. The circadian blood pressure rhythm, which showed a normal pattern during the daytime work shift, was totally reversed from the first day of the night shift. The blood pressure rhythm closely followed the sleep-wakefulness cycle. The changes in circadian heart rate rhythm were not as pronounced as those in blood pressure but showed a similar trend.