The bronchodilator effects of a single dose of ipratropium bromide aerosol (36 micrograms) and short-acting theophylline tablets (dose titrated to produce serum levels of 10-20 micrograms/mL) were compared in a double-blind, placebo-controlled crossover study in 21 patients with stable, chronic obstructive pulmonary disease. Mean peak forced expiratory volume in 1 second (FEV1) increases over baseline and the proportion of patients attaining at least a 15% increase in the FEV1 (responders) were 31% and 90%, respectively, for ipratropium and 17% and 50%, respectively, for theophylline. The average FEV1 increases during the 6-hour observation period were 18% for ipratropium and 8% for theophylline. The mean duration of action was 3.8 hours with ipratropium and 2.4 hours with theophylline. While side effects were rare, those experienced after theophylline use did involve the cardiovascular and gastrointestinal systems. These results show that ipratropium is a more potent bronchodilator than oral theophylline in patients with chronic airflow obstruction.