Changes induced by nifedipine (10 mg s.l.) in the residual lumen diameter of significant (greater than 50%) coronary lesions were assessed angiographically in 69 patients with effort angina (Group 1), in 22 patients with mixed angina (Group 2), and in 14 patients with Prinzmental angina (Group 3). These changes were related to the clinical response to treatment with the same drug (diary records, exercise testing, Holter monitoring). In Groups 1 and 2 segments of stenotic vessels showed either increase, decrease or no change in diameter with the calcium antagonist; in Group 3 the majority of the vessels showed compliant portions which invariably responded with dilatation. Nifedipine failed to improve cases with exertional (21% unchanged, 19% worsened) and mixed (41% exacerbated) forms; all patients with the Prinzmental form had relief of the anginal episodes. In Group 1, the response to exercise tests were dissociated from the acute vasomotor pattern and the pressure-rate product failed to explain the clinical results. Fifty-two percent of the patients in Group 2 showed significant acute widening of critical stenoses as well as obvious improvement; patients in this group who did worse with treatment had reacted to nifedipine with narrowing of their critical stenoses. These data suggest that: the response to nifedipine of classic effort angina is probably the net result of an interaction of changes in myocardial oxygen consumption and supply; coronary vasomotion has a role in mixed angina and influences of nifedipine may be either favorable or unfavorable; stenotic lesions in the Prinzmental form are quite sensitive to the relaxant action of calcium blockade and this probably represents a background to the highly positive clinical response to treatment.