The purpose of this study was to determine whether the early stages of arterial atherosclerosis could be evaluated by the vascular response to nitroglycerin (NTG). The vascular elasticity of the common carotid artery (CCA) was evaluated at sites without atheromatous plaque using high-resolution ultrasonography before and after sublingular NTG administration. The vascular elasticity was expressed by vascular strain (VS) and pressure-strain elastic modulus (Ep). The study was performed in 9 normal young males (group N) and 52 patients who were suspected to have coronary artery disease (CAD). In group N, VS of the CCA increased from 9±2 to 13±4%, Ep decreased from 80±18 to 42±14 kPa (p<0.01) and systolic blood pressure (SBP) decreased from 116±8 to 109±8 mmHg (p<0.05) after NTG administration. Two different responses were observed in the patients. One group of patients (group A, n=27) showed similar responses to NTG as those of group N; that is, VS increased from 8±4 to 14±8%, Ep decreased from 115±64 to 57±31 kPa (p<0.01) and SBP decreased from 121±15 to 110±16 mmHg (p<0.05). In the other group (group B, n=25), in spite of SBP decreasing from 124±21 to 111±21 mmHg (p<0.05), VS decreased from 11±4 to 7±3% and Ep increased from 76±29 to 113±53 kPa (p<0.01). The prevalence and severity of CAD were lower in group A than in group B (33 vs 80%, 11 vs 60%, p<0.01, respectively). The prevalence of atheromatous plaque of the CCA was also lower in group A than in group B (4 vs 22%, p<0.01). These results revealed that the prevalence of carotid atheromatous plaque was highly correlated with that of CAD (p=0.001) and suggested that the vascular elasticity response of the CCA to NTG is highly associated with atherosclerotic changes of the artery and may be a useful method for detecting the early stages of atherosclerosis. (Jpn Circ J 1998; 62: 494 - 498)