Asthmatic bronchitis is a term that encompasses a large number of patients who generally smoke cigarettes and demonstrates chronic mucous hypersecretion and airway hyperreactivity. These patients are frequently labelled simply as asthmatic. In this setting, however, "asthma" is a nonspecific term applied to patients with a variety of symptoms. On the basis of history, bronchodilator response, and response to bronchoprovocating agents, it is frequently difficult to differentiate between groups of chronic bronchitics and asthmatics. Subjects with chronic bronchitis clearly demonstrate bronchial hyperreactivity to bronchoprovocating agents. This response does not appear to be due to an abnormality in bronchial smooth muscle. Chronic bronchitics may also respond to a variety of bronchodilating agents, again demonstrating the presence of bronchial hyperreactivity. Potential mechanisms for the observed bronchial hyperreactivity include reduced airway caliber, reduced resistance to airway narrowing, and airway inflammation. Airway inflammation may be the common link between airflow obstruction and airway hyperreactivity frequently seen in these patients. The finding of airway hyperreactivity in chronic bronchitis has implications far beyond simple therapeutic considerations and may lead to a better understanding of bronchial hyperreactivity under any circumstance.