The relationship of age and prechallenge FEV1 to methacholine airway responsiveness was examined among 914 male participants of the Normative Aging Study (age range 41 to 86 yr). Methacholine airway responsiveness was analyzed as both a continuous (dose-response slope) and categorical (PD20 FEV1 greater than 8.6 mumol; PD20 FEV1 less than or equal to 8.6 mumol) variable. Methacholine responsiveness, as assessed by dose-response slope, displayed a significant inverse relationship to the prechallenge level of FEV1 (p less than 0.001). The dose-response slope was directly related to age among former smokers (p = 0.003) but not among current and never smokers. Using a categorical variable rather than the dose-response slope to characterize responder status yielded very similar results. A logistic regression model of the data predicts an approximately threefold greater odds of a positive methacholine challenge test in association with a 500 ml lower FEV1. The model predicts that among former smokers a 20-yr increase in age is associated with an approximately fivefold increase in the odds of a positive methacholine challenge test. This analysis suggests that nonspecific airway responsiveness increases with advancing age among former smokers even after adjustment for prechallenge level of FEV1.