The efficacy, persistence of bronchodilator action, and safety of the quaternary ammonium anticholinergic agent, ipratropium bromide (500 microgram), and placebo were compared when each was added in solution form to the beta-adrenergic agonist solution, metaproterenol sulfate (15 mg), and administered three times daily for 12 weeks to a total of 213 patients with chronic obstructive pulmonary disease (COPD). Subjects had a mean forced expiratory volume in 1 second (FEV1) of approximately 1 liter (37% of predicted) and were permitted to use nonanticholinergic therapy for COPD throughout the trial. The study was a randomized, double-blind, 85-day, parallel-group, eight-center study. On a 3 test days, 1, 43, and 85, mean peak responses for FEV1 and forced vital capacity and mean area under the curve were significantly higher for the iprathropium bromide-metaproterenol combination than for metaproterenol only. Duration of action was also significantly longer for the combination therapy than for the beta-agonist alone on test days 1 and 43. Neither treatment regimen produced an demonstrable effect on daily morning peak expiratory flow rates, reported respiratory symptoms, or quality of life. Both treatment regimens were similarly well tolerated with a comparable frequency of adverse events. These results suggest that the combination of iprathropium bromide and metaproterenol inhalation solutions offers a potential therapeutic advantage to patients with symptomatic COPD over nebulized metaproterenol alone without the risk of increased side effects.