The effects of inhaling an aerosol preparation containing fenoterol 200 micrograms and ipratropium bromide 80 micrograms were compared with those of inhaling 200 micrograms of salbutamol and a similar dose of fenoterol on 20 patients with chronic bronchitis and four patients with chronic stable asthma. The dose of each drug was contained in 2 puffs taken from a metered-dose inhaler. Changes in airways function were assessed by measuring peak expiratory flow rate. Pulse, blood pressure and presence of any tremor were monitored to detect drug-induced side effects. No significant difference was found in the onset of action and overall bronchodilator effects between the three drugs. The combined preparation was found to have a significantly greater bronchodilator action three and four hours after inhalation compared to the other two drugs. A significant effect lasting six hours was found with salbutamol and fenoterol, but the combined preparation had an effect which was significant up to seven hours. There was no significant difference in the side effects which were minimal for all three drugs.