The accuracy, rapidity, and reproducibility of color-Doppler-assisted duplex sonography in the diagnosis of significant internal carotid artery stenosis were prospectively evaluated. Only the point of maximal color shift on the color map was used for spectral analysis. When compared with angiography in 60 carotid bifurcations, a measured peak systolic velocity above 1.25 m/sec was 87% accurate in the detection of significant internal carotid artery stenoses greater than 50%. Determination of maximal internal carotid artery velocity was 40% faster with color-Doppler-assisted duplex sonography than with nonassisted duplex ultrasound. The correlation coefficient for interobserver agreement was .90. It increased to .97 when cases of extensive (greater than 1 cm) acoustic shadowing (7% of bifurcations) were excluded. The authors conclude that the color flow map is an accurate and reproducible means of depicting the point of maximal stenosis within the internal carotid artery.