Background The aim of the present study was to assess the feasibility and usefulness of the arterial stiffness index (ASI) measured non-invasively by computerized oscillometry and by comparing it with the pulse wave velocity (PWV). Methods and Results The study group comprised 60 consutive patients who underwent coronary angiography and whose aorto-femoral PWV were obtained with a Judkins catheter. The ASI was obtained using Cardio Vision ^® MS-2000 (IMDP, Las Vegas, NV, USA): (i) baseline (ASI-B); (ii) hyperemia induced by compression of the arm with cuff pressure for 5 min (ASI-H); and (iii) sublingual nitroglycerin (ASI-N). In total, 34 patients had significant coronary artery disease (CAD). The PWV and all ASI were higher in patients with CAD than in those without CAD (ASI-B, 85.9±57.8 vs 48.2±24.5, p=0.001; ASI-H, 98.1±49.8 vs 48.1±21.3, p<0.01; ASI-N, 66.7±55.7 vs 33.2±27.9, p=0.002). However, only ASI-B and ASI-H were positively correlated to the PWV (ASI-B, r=0.27, p=0.03; ASI-H, r=0.49, p=0.001; ASI-N, r=0.19, p=0.16). The ASI was increased after hyperemia in patients with CAD (ASI-H, 85.9±57.8 to 98.1±49.8, p=0.01), but not in patients without CAD (ASI-H, 48.2±24.5 to 48.1±21.3, p>0.01). After adjusting their age, only ASI-H was correlated to the presence of CAD (r=0.33, p<0.01). Conclusions It is feasible and useful to use the ASI for detection of atherosclerotic coronary disease. The findings of ASI-H suggests that in addition to stiffening of the arterial wall itself, the impairment of flow mediated vasodilation, because of endothelial dysfunction, further increases the arterial stiffness. (Circ J 2005; 69: 1218 - 1222)