The search for a practical, clinically applicable system for non-invasive detection and diagnosis of atherosclerosis followed early demonstrations that ultrasound could be used. Pulse-echo systems were the first to be investigated and showed that, although plaque could be visualized or its absorption properties made apparent in vivo, some types of plaque would not be visualizable[l]. Apparently, fatty plaque or plaque whose blood tissue interface was not at right angles to the sound beam could not be differentiated from blood. Interest was then focused on imaging of the blood itself through various types of imaging systems based on the ultrasonic Doppler effect. The first of these was a pulse-Doppler system which produced cross-section flow images [2]. The present authors developed a continuous wave (c-w) Doppler system which, by ignoring the depth coordinate, produced a plan view geometrically similar to an arteriogram [3]. The c-w system to be described here was devised as a clinically-applicable screening tool for diagnosis of surgically correctable flow disturbance in large arteries. It has been applied to the carotid and vertebral arteries of the neck and evaluated on more than 3,000 patients in our clinics alone. Other centers have reported active use of this equipment [4, 5].