Several plants are used in traditional medicine for the treatment of bronchial asthma. We are trying to identify the active compound(s) and their mode of action. For the isolation and identification of the active principles, different chromatographic methods, HPLC, MPLC, elementary analysis, UV, mass, 1H- and 13C-NMR spectroscopy are used. Whole plant extracts, fractionated extracts and pure compounds are tested in the following pharmacological systems: cyclooxygenase and lipoxygenase pathway of arachidonic acid metabolism, bronchial obstruction of guinea pigs after inhalation of allergens, platelet-activating factor (PAF), histamine or acetylcholine, PAF-induced bronchial hyperreactivity of guinea pigs, histamine release, chemoluminescence and chemotaxis of human polymorphonuclear leukocytes as well as thromboxane biosynthesis of human platelets. As active compounds in onion extracts, thiosulfinates and cepaenes could be identified. They exert a wide spectrum of pharmacologic activities, both in vitro and in vivo. Tetragalloyl quinic acid from Galphimia glauca, suppressed allergen- and PAF-induced bronchial obstruction, PAF-induced bronchial hyperreactivity (5 mg/kg orally) in vivo and thromboxane biosynthesis in vitro. Hitherto unknown alkaloids from Adhatoda vasica showed pronounced protection against allergen-induced bronchial obstruction in guinea pigs (10 mg/ml aerosol). Androsin from Picrorhiza kurroa prevented allergen- and PAF-induced bronchial obstruction (10 mg/kg orally; 0.5 mg inhalative). Histamine release in vitro was inhibited by other compounds of the plant extract yet to be identified. Pharmacological effects of plant extracts and pure compounds in man are under investigation.