Salbutamol in a powder aerosol from the Rotahaler insufflator was compared, with equal doses of the conventional pressurized aerosol by dose-response curves and in a 1 month open trial, in the treatment of asthma patients with good inhalation technique. Results were not significantly different in either study. A further group of asthma patients, who were known to be incapable of using pressurized aerosols effectively, were shown to benefit from treatment with the Rotahaler. This device should increase the value of the sympathomimetic drugs to the minority of asthma patients who cannot use conventional aerosols correctly.