Coronary spasm provocation by intracoronary methylergonovine was performed in 14 patients (8 men and 6 women, mean age 56 +/- 6 years) with syncope that remained unexplained despite neurologic and noninvasive cardiac evaluations. Electrophysiologic testing was also performed in 6 of 14 patients. No patient had structural heart disease or significant fixed stenosis of greater than or equal to 75% in the coronary arteries. Six patients had no history of chest pain even when they developed syncope. Serious arrhythmia was documented in 2 patients, cardiac standstill in 1 and complete atrioventricular block in the other. Coronary spasm was induced in 9 patients using the methylergonovine provocation test. Multivessel spasms were found in 3 patients. Coronary spasm was induced in the artery supplying the inferior wall in 7 of 9 patients with positive results. In 4 of 9 patients who had a positive result, there was no prior history of chest pain. In 1 patient, whose electrocardiogram was recorded during syncope, cardiac standstill was documented and cardiac standstill and syncope also occurred during the provocation test. Monomorphic ventricular tachycardia was not induced by the electrophysiologic study. These results suggest that coronary spasm is involved in unexplained syncope.