The marked increase in cardiovascular events that occur in the early morning hours could be related to a significant rise in blood pressure at this time but there is uncertainty as to whether this rise in pressure occurs before, at, or after awakening. Automatic blood pressure and pulse measurements were taken twice on 15 normotensive subjects and three times on 11 untreated hypertensive subjects starting before the onset of sleep and at 10 min intervals for 1 h before and 60 to 90 min after awakening. In random order, all subjects either remained supine or immediately arose and ambulated on the first two occasions. The hypertensives had a third study involving ingestion of 10 mg nifedipine after awakening and remaining supine for the next 60 min. The blood pressure and pulse changed little before and after awakening if the subjects remained supine. They rose rapidly and significantly immediately upon arising. The rise in pressure upon arising was blunted by the prior ingestion of nifedipine. The early morning rise in blood pressure and pulse is mainly related to arising from bed. Possible ways to reduce the abrupt rise in blood pressure and the increase in cardiovascular events that occur after arising are suggested.