103 patients with acute airflow obstruction (56 asthma, 47 chronic obstructive pulmonary disease [COPD]) completed a double-blind trial of nebulised bronchodilator treatment in a hospital accident and emergency department. Each patient was randomised to receive either 10 mg of salbutamol nebuliser solution in 2 ml of saline or 10 mg of salbutamol in 2 ml (0.5 mg) of preservative-free ipratropium bromide. Peak flow rate (PFR) was recorded before treatment and 1 hour after beginning nebulised treatment. In 23 asthmatic patients given salbutamol alone PFR rose by a mean 31% 1 hour after treatment whereas in 33 such patients given combined treatment it rose by a mean 77% (95% confidence interval for the difference 8-84%). Patients whose PFR was below 140 l/min at entry gained maximum benefit from the combined treatment. For COPD patients the PFR rise was almost identical for both treatments. In acute asthma the immediate PFR response to a mixture of salbutamol and ipratropium bromide was better than the response to nebulised salbutamol alone. For COPD patients, the two treatments were of equal benefit.