Inhaled antiasthmatic agents can be effective, but their efficacy depends on the delivery system and on inhalation technique, especially in metered-dose inhalers (MDI). To find out whether inhalation therapy for asthmatics had been performed correctly, we studied inspiratory flow in the slow matter in healthy subjects and bronchial asthma patients. About half of 30 patients studied inspired more than 1 L/sec inspiratory flow rate, especially in male. Inspiratory flow in the fast matter (peak inspiratory flow; PIF) is important in the use of dry powder inhaler, so we studied the correlationship between PIF and expiratory flow and volume parameters. PIF correlated with PEFR, FEV1 and FEV1% in female, FVC and %FVC in male, respectively. In summary, we must recognize slow inspiratory flow can not be gotten easily, and asthmatic patients always have to use MDI carefully in inspiratory flow. Some expiratory parameters of spirometry can accurately predict PIF. The analysis of inspiratory flow-volume curve gives us beneficial data in inhalation therapy.