Quaternary anticholinergic bronchodilators offer gradual and sustained bronchodilation to patients who have asthma or chronic obstructive pulmonary disease. For asthma, the anticholinergic compounds are less potent than the beta-adrenergic agents but have useful additive bronchodilator properties when combined with beta-adrenergic agents or theophylline. They may be particularly useful in combination regimens for patients who have severe asthma and for older asthmatics. The rationale for such a combination is most compelling in the treatment of acute exacerbations of asthma. For chronic obstructive pulmonary disease, anticholinergic compounds offer greater bronchodilation than beta-adrenergic agents for most patients and are thus considered useful initial therapy in maintenance regimens.