Asthma and chronic bronchitis are among the most common chronic diseases afflicting middle-aged and elderly adults in the United States, respectively occurring in 4 percent and 5 percent of the population in these age groups. While chronic bronchitis is often caused by cigarette smoking and asthma often occurs in nonsmokers in association with atopy, the two conditions may be difficult to differentiate in many middle-aged and older adults and may share a number of pathophysiologic features including increased airway smooth muscle tone, increased airway responsiveness to bronchoconstricting stimuli, and bronchial mucus hypersecretion. The precise mechanisms which produce the alterations of airway function are not clear. Such functional alterations may be caused by airway inflammation and abnormalities of the autonomic nervous system; however, there are little population data available regarding the importance of airway inflammation and disordered neural regulation in the pathogenesis of airway hyperresponsiveness and mucus hypersecretion. Also, little is known about potential interactions between airway inflammation and disordered neural regulation of airway function in the pathogenesis of chronic airways disease. Information on the relationships may offer insights into the pathophysiologic mechanisms underlying asthma and chronic bronchitis in adults.