BACKGROUND There have been numerous studies in asthmatic adults demonstrating the efficacy and safety of bitolterol mesylate metered-dose inhaler; however, only one additional study has examined bitolterol metered-dose inhaler in pediatric asthma. OBJECTIVE To establish the safety and effectiveness of bitolterol mesylate metered-dose inhaler at one, two, and three inhalations in pediatric asthmatic patients 4 to 12 years of age. METHODS A multicenter, double-blind, randomized, crossover, placebo-controlled, dose-ranging study. Forty-six patients were evaluated in three centers. Patients were stratified by age, 4 to 6, 7 to 9, 10 to 12 years at each center. One, two, or three inhalations were administered along with an additional double-blind, randomized, placebo dose. Bronchodilation was defined as a 15% or greater increase in FEV1 over baseline. Onset, maximum improvement, and duration of action were obtained for each patient. Serial pulse rate, blood pressure, and respiratory rate determinations were obtained for each patient. RESULTS Onset within five minutes occurred in 56.6% to 71% of patients, depending on the dose. Mean maximum improvement, which was dose dependent, overall ranged from 28.2% to 40.3% with a peak response in 66.7 to 69.8 minutes. In direct relationship of magnitude with regard to dose of bitolterol was observed, (P < .001). A significant correlation, r = .732, in response between bronchodilation and baseline FEV1 was observed (P < .001). Median duration of action ranged from three to four hours in responding patients across all doses. Up to 31% of patients had durations greater than eight hours after three inhalations. Adverse effects were reported in five of 46 patients for all doses with mild transient tremor occurring in two patients, 4.3%. Also, there was little effect on pulse rate, 2.2%. CONCLUSIONS Bitolterol is an effective bronchodilator with durations of activity up to eight hours and minimal adverse effects in children.