It is unclear whether obesity is associated with increasing degree of airway responsiveness in asthmatics. In this study, methacholine challenge test results of 1,725 subjects with respiratory symptoms were reviewed. Obesity was associated with asthma with an odds ratio of 1.72 (95% C.I. 1.36, 2.17). Although there was a significant difference in the degree of airway responsiveness between various body mass index categories of non-asthmatics (p = 0.01), no significant difference was noted among asthmatics (p = 0.93). A weakly significant interaction between asthma status and body mass index on the degree of airway responsiveness was noted (p = 0.08).