We investigated the effect of 300 micrograms of inhaled beclomethasone dipropionate (BDP) daily on bronchial responsiveness to methacholine and pulmonary function of 22 subjects with asthma in a single-blind, crossover study. The severity of bronchial hyperresponsiveness lessened significantly during treatment with BDP (P < .01). No significant changes occurred in FEV1 or in the control value of airway conductance. We conclude that a 300-micrograms total daily dose of BDP is an efficacious treatment for patients with asthma. Because suppression of adrenal function and systemic adverse effects can occur in asthmatic patients treated with inhaled corticosteroids, especially children, long-term treatment with inhaled steroids should employ minimal daily doses necessary.