Bronchial responsiveness to methacholine was studied in 23 stable asthmatics before and after nifedipine and diltiazem. There was no significant bronchodilatory effect of either calcium channel antagonists. The mean provocative dose of methacholine required to produce a 20% fall in FEV1 (PC20 = 0.157 +/- 0.74 mg) was not altered by nifedipine (PC20 = 0.159 +/- 0.61). However, diltiazem offered significant protection. The mean ratio of PC20 after diltiazem over baseline was 3.27 +/- 3.55. The results suggest that although both calcium channel antagonists have no influence on normal basal bronchomotor tone, diltiazem does significantly protect against cholinergic stimulation.