The efficacy of the selective beta 2 sympathomimetic fenoterol (Berotec) in aerosol and tablet forms was studied in 15 subjects with reversible airways obstruction. The maximal bronchodilator effect of fenoterol by aerosol (0.4mg) was found to equal that of isoprenaline, and to be maintained at that level over the three hour period studied. When given orally, neither one tablet (2.5 mg) nor two tablets (5 mg) of fenoterol increased the FEV1 to the same extent as isoprenaline, and the larger oral dose (5 mg) produced troublesome side effects in several subjects. It is concluded that fenoterol by aerosol is an effective bronchodilator with a duration of action of at least three hours, without significant side effects.