Background: We investigated the complications of spasm provocation tests, including acetylcholine (ACh) tests, ergonovine (ER) tests and adding ACh after ER tests, retrospectively. Methods: We performed 1546 ACh tests and 1114 ER tests during 23 years, including 240 adding ACh after ER tests. ACh (RCA: 20/50/(80) g, LCA: 20/50/100/(200) g) was injected incrementally over 20 seconds, whereas ER (RCA: 40 g, LCA: 64 g) was administered over 2-4 minutes. In addition, we administered adding intracoronary injection of ACh (RCA: 50/80 g, LCA: 100/200 g) after ER tests. Serious major complications were defined as ventricular fibrillation, sustained ventricular tachycardia, shock, severe hypotension (< 60 mmHg), cardiac arrest and cardiac tamponade. Results: Serious major and major complications were higher in ACh tests than ER tests (1.8% vs. 0.4%, p<0.01), whereas serious major complications were not different between ACh and ER tests (0.9% vs. 0.4%, ns). No serious major or major complications were observed in adding ACh after ER tests. Paroxysmal atrial fibrillation was not different between ACh tests and adding ACh after ER tests (16.7% vs. 12.5%, ns). Necessity of nitrates to relive provoked spasms prior to carrying other site tests were significantly higher in ER tests (6.8%) than ACh tests (2.0%) and adding ACh after ER test (2.5%). No death or irreversible complications were recognized in all three spasm provocation tests. Conclusions: Serious major complications were not different between the two agents, whereas serious major and major complications were significantly higher in ACh tests than ER tests. Although pharmacological spasm provocation tests including adding ACh after ER tests were reliable and relatively safer methods, we should perform these tests positively in the cardiac catheterization laboratory.