Twenty patients with asthma were studied. They were given either fenoterol powder or fenoterol MDI for 2-week periods using a double-blind cross-over design. Identical doses of fenoterol (0.2-0.4 mg 2-4 times daily) were given to an individual patient throughout the 4-week study period. Both forms of treatment produced an almost identical bronchodilation, and there were no statistically significant differences in symptoms or side effects. It is concluded that fenoterol powder and fenoterol aerosol are equally effective.