A 47-year-old black male who presented with classical angina pectoris and positive exercise test developed spasm of the right coronary artery in the vicinity of an atherosclerotic lesion resulting in transient total occlusion of the vessel. It seemed unlikely that spasm was catheter induced in this case, and the vessel relaxed promptly following nitroglycerin administration. The occurrence of severe spasm in proximity to atherosclerotic narrowing of coronary artery may contribute to stable and unstable angina, myocardial infaction, and sudden death in patients with these conditions coexisting. The awareness of such a phenomenon is necessary to avoid serious errors in the interpretation of coronary angiograms.