Patients with COPD may respond differently to anticholinergic and beta-agonist bronchodilators. Previously, in acutely ill COPD patients, we showed similar improvements in pulmonary function after each drug (study 1). The responses of the same patients when stable are now reported (study 2). Patients received ipratropium bromide (54 micrograms) (n = 16) or metaproterenol sulfate (1.95 mg) (n = 14) via an MDI attached to a delivery device as in study 1. Ninety minutes after the first medication, patients received the second. Spirometry was measured at entry and at 30-min intervals following the first drug and at the same times after the second drug. Results were as follow: The groups did not differ in clinical characteristics. However, for both groups, there was significantly less airway obstruction at entry into study 2. In study 1, ipratropium resulted in significant improvement in FEV1 (0.62 +/- .08 to 0.88 +/- .11 L; mean increase 24 percent; p less than 0.05) with no further change after crossover. In study 2, ipratropium produced similar improvements in FEV1 by 90 minutes (0.94 +/- .09 to 1.3 +/- .09 L; mean increase 25 percent; p less than 0.05), with no further improvement after crossover. For metaproterenol, in study 1, the improvement in FEV1 was not significantly different than that for ipratropium (FEV1; 0.71 +/- .07 to 0.92 +/- 0.06 L; mean increase 18 percent; p less than 0.05), with no further improvement after crossover. In study 2, improvement with metaproterenol was significant and similar to study 1 (FEV1: 0.96 +/- .06 to 1.21 +/- .09 L; mean increase 18 percent; p less than 0.05). Thus, ipratropium and metaproterenol similarly improved pulmonary function in COPD patients when stable and during acute exacerbations.