The purpose of this study was to determine the intensity and duration of the protective effect of fenoterol (200 micrograms) in allergen-induced bronchospasm and to compare its effect with that of DSCG (20 mg). Twelve atopic-asthmatic patients, with ages ranging from 10 to 41 years, participated in the study. At the time of the study their symptoms were well controlled without the use of anti-asthmatic drugs and their FEV1 was greater than 80% of predicted and did not vary by more than 10% on each study day. The study was a double-blind cross over trial. Each drug was given separately at 1 week intervals according to an appropriate random plan. During the treatment the patients were given two puffs of metered dose aerosol and a capsule of inhalation powder. Each patient was given aerosol with test drug and placebo aerosol alternately, according to the double-blind method. The allergen was given 90 min after the administration of the drugs, and parameters of the respiratory function were controlled over a period of 6 h. Subsequently, the protective effect of 200 micrograms fenoterol administered 4 h before the allergen was studied openly, and showed that fenoterol possesses a protective effect in allergen-induced bronchospasm. This effect, although slightly reduced, persists even when the allergen is administered 4 h later.