Since there have been only a few studies on muscarinic receptor subtypes in airway smooth muscle, the effect was investigated of pirenzepine on airways of patients with chronic obstructive pulmonary disease (COPD) and the functional responses compared from these patients with those from healthy subjects. Our data demonstrated that the therapy with pirenzepine significantly improved ventilatory function in patients with COPD. The data also suggested that this drug exerts its action on small airways, but not larger airways in normal subjects. It is possible that in healthy human beings pirenzepine produces mild bronchodilation by means of a vagal efferent blockade, while in patients with COPD, it may be effective because it not only decreases the activity of the vagal efferent pathway, but also decreases the sensitivity of vagal sensory endings and causes a vagal afferent blockade.