Deep inspirations have the ability to dilate constricted airways. The impairment of this function has been associated with the occurrence of asthmatic symptoms. We evaluated whether the bronchodilatory effect of deep inspiration (DI) is affected by aging. We tested 25 healthy subjects (median age: 54 yrs, range: 25-83 yrs). Single dose methacholine (Mch) provocations were performed in the absence of DI, which induced at least 15% reduction in inspiratory vital capacity (IVC) from baseline. The post-Mch IVC measurement was followed by 4 DIs and by another IVC (post-DI IVC). The fractional difference between post-DI IVC and post-Mch IVC represented the % bronchodilation by DI. The % bronchodilation significantly diminished with aging (r=0.65, P=0.0005). The bronchodilatory ability of DI was also positively associated with the degree of Mch-induced reduction in IVC (r=0.84, P<0.0001). In multiple regression analysis, where % bronchodilation was the dependent variable, both % reduction in IVC (P<0.0001) and age (P=0.02) entered the model. Our data raise the hypothesis that aging is associated with reduction in DI-induced bronchodilation.