Background: Intracoronary injection of acetylcholine (Ach) has been shown to induce coronary spasm in patients with variant angina. Clinical significance and angiographic characteristics of patients (pts) with (+) provocation results to low Ach dose are not clarified yet as compared with pts respond to high Ach dose. Methods: A total 3034 consecutive pts underwent coronary angiography Ach provocation tests from January 2004 to August 2010 were enrolled for this study. Ach was injected in incremental doses of 20, 50, 100��� into the left coronary artery. Significant coronary artery spasm (CAS) was defined as focal or diffuse severe transient luminal narrowing (>70%) with/without chest pain or ST-T change on ECG. A total 1445 pts (47.6%) showed positive provocation tests. We compared the clinical and angiographic characteristics of patients responded to low dose (20���) to those to high dose (50���). Results: The baseline clinical and procedural characteristics are well balanced between the two groups. There was no difference in the incidence of myocardial bridges in both groups. Low Ach dose spasm group showed more frequent ischemic ECG changes and atrioventricular (AV) block on ECG during the Ach provocation test. Further, the pts with Low Ach dose group was associated with higher incidence of baseline spasm, severe vasospasm, multi-vessels involvements, and a trend toward more diffuse spasms (>30mm) than those with the High dose group (Table). Conclusion: The pts significantly respond to low Ach dose were associated with more diffuse, severe and multivessel spasm than pts respond to high dose, suggesting more intensive medical therapy with close clinical follow up will be required for these patients.