1. The morning rise in blood pressure and heart rate was studied in 18 patients with mild blood pressure elevation. Passing from sleep to the drowsy state raised blood pressure and heart rate very little while the awake state (reading a newspaper sitting in bed) increased the mean blood pressure by 13.2 mm Hg and the heart rate by 5.7 beats per minute. 2. Subsequent application of mental stress (arithmetic) in one third of the patients or physical activity in the upright position in another third showed a different pattern of response. Mental stress mainly raised the blood pressure while physical activity in the upright position mainly raised the heart rate.