We compared the basal coronary artery tone and the constrictive responses to acetylcholine (Ach) and ergonovine (Erg) among three groups of patients: 31 patients (group 1) with variant angina in whom spasm was provoked by low doses of acetylcholine (intracoronary 20 micrograms) or ergonovine (intravenous 50 micrograms); 35 patients (group 2) in whom spasm was provoked by higher doses of acetylcholine (intracoronary 100 micrograms) or ergonovine (intravenous cumulative dose of 350 micrograms); and 26 control subjects. Patients with variant angina in whom spasm was provoked by low doses of acetylcholine or ergonovine, had a higher incidence of coexisting angiographic evidence of coronary artery disease, multi-vessel spasm and more frequent episodes of angina. The basal coronary artery tone at the spastic and non-spastic sites of the spasm-related artery was significantly elevated in group 1 compared to group 2 (44 +/- 17 vs. 14 +/- 11% and 26 +/- 14 vs. 16 +/- 10%, respectively, P < 0.05), but not in the non-spasm related artery. The magnitude of vasoconstrictive responses to acetylcholine and ergonovine at the non-spastic sites was also greater in group 1 than in group 2 and the control groups (acetylcholine: 40 +/- 20 vs. 26 +/- 11, 27 +/- 12%; ergonovine: 37 +/- 18 vs. 12 +/- 8, 13 +/- 10%, respectively, P < 0.05). However, the basal coronary artery tone was not elevated at the spastic and non-spastic sites in group 2 compared to that in the control subjects. These findings suggest that the basal coronary artery tone is increased in patients with variant angina, with increased frequency of angina suggestive of higher disease activity at the spastic and non-spastic sites of the spasm-related artery, and this may be related to pathogenesis of coronary artery spasm.