The anticholinergic, antimuscarinic compounds are potent and hitherto neglected bronchodilators. Although atropine itself has drawbacks, principally related to its rapid absorption and consequent systemic side effects, its quaternary ammonium congeners, atropine methonitrate and ipratropium bromide, are poorly absorbed. When given by inhalation, they are as effective bronchodilators as atropine is, but longer acting and much less prone to side effects. They act predominantly at a site that is different from adrenergic agents and thus afford an alternative, complementary approach to the treatment of airways obstruction. In stable asthmatic subjects, ipratropium is almost as potent a bronchodilator as beta 2-adrenergic agents are. In patients with chronic bronchitis and emphysema, it is more potent than beta 2-adrenergic agents are. In both conditions, its combination with other bronchodilators adds significantly to the level and duration of bronchodilatation. It may also be occasionally useful in counteracting bronchospasm caused by specific stimuli, such as cold air and exercise, and particularly that caused by inadvertent beta-adrenergic blockade. By inhalation, ipratropium is relatively free of side effects, even in doses as much as 20 times those that produce maximal bronchodilatation. It does not significantly affect mucus production, viscosity, or clearance, problems for which atropine is suspect. Nor does it produce tremor and tachycardia, as do adrenergic agents. It can also probably be safely used in patients with glaucoma and bladder neck obstruction, unlike atropine. Ipratropium will probably find its major application in the long-term management of chronic bronchitis and emphysema, and in asthmatic patients who are poorly controlled by, or who experience troublesome side effects from, adrenergic agents.