In a double-blind cross-over study, 12 patients with reversible airways obstruction were treated with 200 micrograms salbutamol base in aerosol or 400 micrograms of powder following methacholine-induced bronchoconstriction. Salbutamol was inhaled either from a conventional metered dose inhaler (MDI) or from an inhaler (Diskhaler) utilizing the powdered form of the drug. The efficacy of both forms was identical whether assessed in terms of FEV1 or vital capacity. The ratio of the increase in FEV1 or vital capacity after bronchodilatation to the decrease during the prior bronchoconstriction was 1.4, indicating that both FEV1 and vital capacity improved over baseline following bronchodilatation. In six subjects, the onset of action of the powder form was more rapid, and in four the MDI acted more rapidly. In the group as a whole, the mean time constant for the action of salbutamol was identical (3.8 min) for the two forms. It is concluded that salbutamol powder has a similar efficacy and time course of action as the aerosol, probably because both formulations produce similar sized particles of the drug.