The blood flow in the vertebral artery was measured in 507 patients with vertigo using ultrasonic blood rheography. In 150 of the 507 cases (32%), abnormal findings including laterality and decreased flow were detected. Twenty-one cases whose clinical course was observed showed a decrease in the differences in velocity between sides as vertigo improved. VBI (vertebro-basilar insufficiency) showed a worse prognosis in patients with laterality compared with those without and a positive correlation was demonstrated between side differences and fluctuating blood pressure or serum lipids. Some anti-vertiginous drugs improved the difference between sides by increasing the velocity.