The correlation of the peak systolic velocity (PSV) and the peak velocity ratio (PVR, calculated as intrastenotic PSV divided by proximally recorded PSV) with percent diameter reduction was studied in 62 patients with peripheral arterial occlusive disease. PSV values correlated well with angiographic diameter reduction (r = 0.81, n = 106 stenoses), but due to large variability the sensitivity and specificity in the detection of greater than 50% stenoses were only 66% and 80% (for a cutoff value of 180 cm/s). The PVR showed less interindividual variability and exhibited a strong correlation with percent diameter reduction (r = 0.93,n = 106 stenoses). A 2.4 fold increase of the peak systolic velocity values with respect to the proximal site (i.e., PVR = 2.4) or more indicated a more than 50% stenosis with a sensitivity of 87% and a specificity of 94%. Figures for PVR are provided to quantitate the degree of stenoses in the 50-99% range. Calculation of PVR may normalize for patient variation and allow noninvasive quantification of lumen narrowing with high sensitivity and specificity.