The purpose of this study was to evaluate the effects of inhaled atropine sulfate on the exercise capacity and cardiopulmonary responses to exercise in patients with chronic airflow obstruction (CAO). Eighteen patients underwent duplicate incremental (15 watts/min) maximal cycle ergometer exercise tests 60 minutes after either inhaled atropine (0.075 mg/kg) or placebo, in double blind randomized fashion on consecutive days. Bronchodilator medications were withheld before each study. Spirograms were obtained before and 60 minutes after each aerosol treatment. Atropine increased the FEV1 by 25 percent, from 1.37 +/- 0.49 to 1.71 +/- 0.52 L (p less than 0.001), as compared to placebo. Although the ventilation at exhaustion (VEmax) increased significantly (from 52.3 +/- 11.5 to 55.9 +/- 10.0 L/min, P less than 0.05) after atropine, the increase in the mean maximum work load (95 +/- 28 vs 101 +/- 19 watts) did not achieve significance. The drug resulted in a significant decrease in oxygen consumption at all equivalent workloads greater than "0" watts (unloaded cycling), presumably because the improvement in airway mechanics decreased the oxygen cost of ventilation. Atropine-induced increases in FEV1 did not result in a significant group mean increase in maximum exercise capacity, but the drug did result in a lower oxygen cost of performing work in patients with CAO.