In 20 patients with proved allergic asthma we investigated the protective action of orciprenaline on bronchial obstruction caused by inhalation of antigen aerosols. In 10 bakers with bronchial obstruction after inhalation of antigen aerosol no subject showed an obstruction when orciprenaline was inhaled previously. In another group of 10 patients (different ubiquitous antigens) only 3 showed a slight increase of airway resistance but lesser than without orciprenaline. After previous inhalation with orciprenaline mostly neither a bronchospasm nor hypersecretion or mucous edema is detectable as bronchial obstruction.