Two series of tests were carried out with 0.5 milligrams of fenoterol, 0.25 milligrams of ipratropium bromide (both by inhalation) and with 240 milligrams of theophylline (intravenously) in persons with extrinsic bronchial asthma. In the first series (A) the broncholytic effects of the drugs were studied by administering them after inhalation provocation tests. In series B the protective effects of the drugs were studied by giving them before the tests. Untreated probands served as controls; in series B 20 milligrams of disodium cromoglicicum were given in addition. The results in series A showed that fenoterol had significantly higher bronchospasmolytic efficacy than the other drugs which were only slightly effective. In series B, however, all four drugs had an equally potent protective action. The results indicate that regular administration of these agents benefits persons with allergic bronchial asthma whereas in acute asthmatic attacks prompt and adequate bronchospasmolysis can be induced only by sympathomimetic drugs with beta-effects.