To investigate the response pattern of patients with chronic airway obstruction (CAO) to bronchodilators, 128 subjects consisting of 80 men and 48 women with a mean age of 52.6 years were randomly tested with three inhalant bronchodilators: a non-selective beta-agonist (isoproterenol), a beta 2-selective agonist (terbutaline) and an anticholinergics (ipratropium) plus placebo. All patients had a baseline FEV/FVC of less than 65% and their clinical diagnosis were classified as either COPD or bronchial asthma according to the criteria of the ACCP-ATS Joint Committee on Pulmonary Nomenclature. The drugs were delivered to the patient via a metered dose inhaler (MDI) using the conventional inhalation technique. Spirometry was measured at regular intervals with a computerized pulmonary function analyzer CHESTAC-65(Japan). A more than 15% increase in FEV1 and/or FVC after treatment was regarded as responsive. While 108 patients were tested with a single drug, the remaining 20 patients were tested sequentially with terbutaline, ipratropium and placebo in a randomized cross-over manner for studying additivity. Our results showed that the response rates of asthmatic patients to isoproterenol, terbutaline and ipratropium were 50%, 87% and 67%, respectively. Only 27% of COPD patients responded to isoproterenol and 60% to terbutaline. On the other hand, ipratropium possessed a 61% response rate in the treatment of COPD and showed a bronchodilator effect independent to that of terbutaline. Combined use of both drugs resulted in additional improvement. Once patients responded to the drugs, apparent changes in FEV1 and/or FVC occurred within 30 minutes and reached the maximum usually at 60 minutes post-inhalation.(ABSTRACT TRUNCATED AT 250 WORDS)