The use of anticholinergic bronchodilators in COPD is based on the reversal of cholinergic bronchomotor tone. There is little information about the magnitude of cholinergic tone in patients with COPD as compared with normal subjects. As an index of the amount of cholinergic tone we measured the maximum increase in FEV1 following administration of an optimal dose of the anticholinergic agent atropine methonitrate. The study included nine normal nonsmoking subjects, ten normal smokers and 22 subjects with mild to moderately severe COPD. We found that normal nonsmokers had smallest increases in FEV1 following atropine methonitrate administration. Responses of subjects with airway disease were progressively greater. Greatest responses occurred in the group of subjects with prebronchodilator FEV1 values less than 55 percent of predicted. The most plausible explanation for this is that cholinergic tone in COPD is increased in proportion to the severity of airway disease. Other explanations are possible.