Patients with chronic obstructive bronchitis commonly suffer acute, transient exacerbations, which suggests that episodic bronchoconstriction may play a role in this disease. We studied 22 patients with chronic obstructive bronchitis and no acute improvement in pulmonary function after inhaled sympathomimetics, using methacholine bronchial provocation tests to evaluate the incidence of bronchial hyperreactivity. Patients with clinical or laboratory findings indicative of asthma were excluded. The group demonstrated significant baseline airway obstruction (mean +/- SD forced expiratory volume in one second, 0.96 +/- 0.44) and no improvement after inhalation of isoproterenol (1.68 +/- 8.54% baseline change). All patients were very sensitive to inhaled methacholine, reacting at a dose of 4.29 +/- 5.49 cumulative units. There were no normal responses. These data suggest that airway hyperreactivity may contribute to acute, transient exacerbations experienced by patients with chronic obstructive bronchitis, even in the absence of acute improvement in pulmonary function after the administration of sympathomimetics, and may warrant chronic prophylactic bronchodilator therapy.