This study was designed to evaluate peak inspiratory flow (PIF) and peak expiratory flow (PEF) in 24 patients with mild asthma. After inhalation of a beta2-stimulant (beta2), PIF significantly increased from 173.0 +/- 67.0 (range 70-300 L/min) to 194.0 +/- 66.7 after 1 minute, and to 199.3 +/- 63.0 after 15 minutes (p < 0.0025, and p < 0.008, respectively). PEF also significantly increased. The previous inhalation of beta2 improved the efficacy of inhalation of dry powder. This evidence should be considered in performing patient education for effective methods of inhalation.