To evaluate the accuracy of Ultrasound Doppler Spectral Analysis (USDA), 432 carotid arteries were examined [group I consisted of 145 cases of normal ICA (internal carotid artery), group II--187 cases of ICA stenosis and group III--100 cases of ICA occlusion]. The maximal systolic peak (Smax), maximal diastolic peak (Dmax), the spectral broadening index (SB) and the pulsativity index (PI) were calculated and related to the degree of stenosis as determined by contrast arteriography. Our results indicate that the change of the value of Smax is the main diagnostic criterion: for carotid arteries' stenoses, it increases to over 3.2 kHz. A Smax over 6.0 kHz is a veritable index of ICA stenosis above 50%: in such cases as the stenosis increases by 10%, this corresponds to an approximately 1 kHz increase of Smax. In ICA occlusion, the main criterion was the absence of blood flow in the distal ICA segment. The UDSA sensitivity in hemodynamically insignificant stenosis is 73.9% which is far higher than in the periorbital Doppler examination; in hemodynamically significant stenosis and ICA occlusions, the sensitivity is 98.6 and 99%, respectively.