We performed a dose-response study of ipratropium bromide as a nebulized solution in patients with stable chronic obstructive pulmonary disease (COPD) using a double-blind crossover format. Five doses from 0.05 to 0.6 mg of ipratropium bromide as a nebulized solution, the standard dose of ipratropium bromide by metered-dose inhaler, 40 micrograms, and placebo were given in random order on separate days. End points were the maximal increase in FEV1 and FVC, and the area under the FEV1 and FVC curves in the 8 h after administration of each of the seven treatments. Forty-two patients completed all seven study days. By each of the above end points for FEV1, 0.4 and 0.6 mg of nebulized ipratropium bromide achieved significantly more bronchodilatation than did each of the other treatments. These two doses were not significantly different from each other, suggesting that the optimal dose in this patient population is 0.4 mg. After this dosage, the FEV1 increased by 440 +/- 194 (mean +/- 1 SD) ml at peak effect between 1 and 2 h, and significant bronchodilatation persisted for 6.5 h. Ipratropium bromide by metered-dose inhaler (40 micrograms) was equivalent to approximately 0.1 mg by nebulized solution and achieved only 63 to 73% of the bronchodilatation achieved by optimal doses of the nebulized solution. In terms of FVC, all treatments with ipratropium were significantly better than with placebo. The area under the FVC curve was significantly greater after 0.4 and 0.6 mg of nebulized solution than after other treatments. No significant adverse experiences occurred with any of the treatments.(ABSTRACT TRUNCATED AT 250 WORDS)