BACKGROUND: Bronchoconstriction associated with aerosolized agents delivered by a metered dose inhaler (MDI) is relatively uncommon, but has been of particular interest. MATERIAL AND METHOD: In this study, we investigated to what extent the inert ingredients and propellants (freons) influence pulmonary function in 25 asthmatic patients. Forced expiratory volume in one second(FEV,) was measured by spirometry, Autospira HI 498(Chest, Japan) before and 1, 3, 5 and 10 minutes after the inhalation of saline control and MDI-placebo containing freons and inert ingredients. RESULT: Twenty four % (6/25) of asthmatics experienced a decrease in FEV20 by 10% or greater when compared to saline control. Number of positive cases in steroid dependent asthmatics is significantly higher compared to non-steroid dependent asthmatics. (p<0.05) Bronchoconstriction associated with the use of MDI-placebo appeared within 3 to 5 minutes and resolved spontaneouly at 10 minutes after the inhalation. CONCLUSION: The bronchoconstrictive response induced by MDI might be caused by the pro-pellants and/or the other inert ingredients contained in MDIs.