To evaluate the role of collaterals in patients with effort angina we retrospectively compared the coronary cineangiograms of 14 subjects ("responders") who improved their exercise tolerance after acute nifedipine therapy with 14 subjects ("non-responders") with the same symptomatology who did not respond to the same treatment. The status of collaterals was graded with a score from a minimum of 0 to a maximum of 5. The responders showed a greater score than the non-responders (3 +/- 1 vs. 1 +/- 1, P less than 0.001), whereas there was no difference in the number of stenosed vessels between the two groups (1.8 +/- 0.9 vs. 2 +/- 0.8). Thus, in patients with effort angina and critical coronary stenosis, the presence of an efficient coronary collateral circulation can favour the increase in coronary flow reserve after vasodilator therapy. Our results suggest that the grading of collaterals may add useful information to the simple classification of one-, two- or three-vessel coronary artery disease.