In 507 vertigo cases in which circulatory velocity in the vertebral artery was determined, using ultrasonic blood rheography, the results in 150 cases (32%) were abnormal, falling appropriately into a 'laterality' group and a 'lower' group. Twenty-one patients whose clinical course was followed up showed a decrease in the side difference of their circulatory velocity, with consequent improvement in their vertigo. VBI demonstrated a poorer prognosis for the laterality group than for the normals, thus indicating a positive correlation between side difference and the effect of fluctuating blood pressure on serum lipids. Certain antivertiginous drugs had a beneficial effect on side difference, increasing the circulatory velocity.