In ten young asthmatic subjects, we studied the effect of a single oral dose of 4.4 mg of azelastine hydrochloride on exercise-induced bronchoconstriction during the breathing of cold air. Exercise challenges were performed on two different days before and four hours after azelastine and placebo given in a randomized double-blind crossover fashion. Placebo had no effect on baseline pulmonary function and postexertional obstruction of the airways, in contrast to azelastine, which exerted a small but significant (p less than 0.05) bronchodilation and a significant attenuation (p less than 0.01) of exercise-induced bronchoconstriction as compared to data from before treatment and after placebo.