Abstract: Plasma DBH changes in 100 cases of acute cerebral vascular accidents （CVA） were observed for 8 weeks. Thirty-one cases among them were admitted within 24 hours alter the onset, the plasma samples were serially collected at least once on the first, second, third, 4th-7th day, and then at least once every week for about 3 weeks. DBH activity in patients with CVA on admission was 28.50±2.39 （mean±S. E.） unit/liter of plasma. It was significantly different from the normal mean activity（36.43±1.50unit/liter, 156 subjects, aged 20—71 years） and the decline of plasma activity was significantly remarkable for about 4 weeks except the second day after the onset. In mild cases, the activity determined on the 3rd-7th day after the onset tended to recover to the initial value obtained within the first 2 days after the onset. On the other hand, in the severe cases a remarkably prolonged decrease of the activity was observed. These data suggest that the activity of the sympathetic nervous system decreases following CVA, and the prognosis of the patients with CVA was closely related to the patterns of time course of plasma DBH after the onset.