Vasa vasorum and the perfusion of the carotid wall in normal arteries and in arteries with arteriosclerotic plaques was evaluated in-vivo using power-Doppler. Two types of arteries were studied using high-resolution ultrasound. These were arteries with a normal wall (intima, media and adventitia clearly separated) and arteries with intima-media thickening and plaques without calcification. In 10 normal subjects and in 10 patients with early plaques vasa vasorum were visualised. On power-Doppler they appeared as distinct, glomerular-like perfusion units, regularly placed along the course of normal arteries and at similar distance (2 to 4 mm from the lumen-wall interface, within the adventitia and periadventitia layers). In arteriosclerotic vessels the distribution of vasa vasorum units was more irregular, often concentrated in one spot with some perfusion units more distant from the lumen (between 2.5 and 5 mm) and their pulsatility was reduced. Flow velocity complex in most vasa vasorum was comparable, in lower scale to the pattern observed in the carotid lumen without significant differences between normal and arteriosclerotic arteries. The average peak systolic flow velocity was 15: +/-4 cm/sec and the average diastolic velocity was 6 +/- 4 in normal arteries with a median pulsatility index of 1.8 (range 2.2-1.05); in arteriosclerotic arteries velocities were 13 +/- 4 (peak systolic) and 3 +/- 2 (end diastolic) with a median pulsatility index of 1.71 (range 2.1-1.1). In conclusion a different, apparent distribution of vasa vasorum was observed in normal carotids and in carotids with arteriosclerotic lesions.