The bronchospasmolytic effects of 40 micrograms ipratropium bromide (Atrovent) given either as an aerosol (2 puffs of 20 micrograms) or as a powder inhalation were compared in a double-blind cross-over study. Following a randomisation list the drug was given on 2 successive days to 20 patients with stable bronchospasm in whom it had previously been shown that the bronchial obstruction was reversible after administration of 40 micrograms ipratropium bromide as an aerosol (with an increase over the baseline value of the FEV1 of at least 15% 1 h after drug administration). The effects of the two presentations of ipratropium bromide were followed by respiratory function tests from 15 min to 6 h after administration of the drug. With both formulations excellent bronchospasmolytic effects were noted in each of the parameters measured. The peak of the effects was noted approximately 1 h after the inhalations. Six hours later there was still a significant improvement in comparison with the baseline values. There was no significant difference between the results with the two different formulations. Inhalation powder of ipratropium bromide was well tolerated and there were no complaints of irritation or coughing. It would appear, therefore, to be a valuable alternative to the pressure aerosol.