Bronchodilators are used widely in the acute exacerbations of chronic obstructive pulmonary disease (COPD), although their effectiveness is not clearly established. We used three bronchodilators in 20 patients with COPD who were being mechanically ventilated. Two of the bronchodilators, ipratropium bromide and salbutamol, were administered from metered-dose inhalers (MDI) through an adapter to the endotracheal tube, and the third, aminophylline, was administered in the form of intravenous infusion. Before administering each drug, peak airway pressure, end-inspiratory pressure, resistive pressure, and auto positive end-expiratory pressure (auto-PEEP) were measured, and inspiratory resistance (Rins) and compliance were calculated. Heart rate (HR) and blood pressure were also recorded, and arterial pH and blood gas determinations were made. These measurements were repeated 60 min after the administration of aminophylline, 15 and 60 min after administering salbutamol, and 30 and 60 min after administering ipratropium bromide. With these three drugs, airway pressures were reduced, as well as auto-PEEP and Rins, with respect to basal values (p less than 0.05). The changes in compliance were only significant with salbutamol (p less than 0.05). HR was only significantly modified with aminophylline (p less than 0.05). No blood gas change was observed with any of the three drugs. It can be concluded that: (1) the three drugs used in this study were equally effective in producing significant bronchodilation in patients on mechanical ventilation for severe acute exacerbation of COPD; (2) the administration of bronchodilators by MDI in intubated patients through a special adapter was as effective as the intravenous administration of aminophylline.