We have investigated the effects of the calcium antagonist nifedipine on antigen-induced bronchoconstriction in vivo and in vitro. Eight grass-pollen-sensitive asthmatics were given either nifedipine (20 mg sublingually) or placebo 30 min before antigen challenge. The fall in forced expiratory volume in one second after pretreatment with placebo was 42.8 +/- 10.1%. After nifedipine this fall was significantly reduced to 26.5 +/- 11.7% (p less than 0.005). Two in vitro models of allergic asthma have been studied: actively sensitized guinea pig tracheal strips (GPT) and passively sensitized human bronchial muscle (HBM). Contraction of GPT by acetylcholine, histamine, and antigen challenge was unaffected by nifedipine 10(-4)M. Contraction of HBM by acetylcholine, histamine and grass pollen antigen challenge was significantly reduced by nifedipine 10(-4)M and 10(-6)M. The magnitude of the reduction in contraction to antigen challenge was comparable to the inhibition of acetylcholine and histamine responses. It would appear most likely that nifedipine exerts its effect mainly on bronchial muscle contractility rather than by stabilizing mast cells.