Flavonoids from Thymus vulgaris L. have been studied in vitro for spasmolytic activity on the smooth muscles of the guinea-pig ileum and trachea and of the rat vas deferens. The flavones and thyme extracts inhibit responses to agonists which stimulate specific receptors (acetylcholine, histamine, L-noradrenaline) as well as to agents whose actions are not mediated via specific receptors (BaCl2). Cumulative dose-response curves point to a non-competitive antagonism. Inhibition of Ca2+ contractions on K+ depolarized smooth muscles suggest inhibition of availability of Ca2+ for muscle contraction. pD'2 values were determined to compare the potency of these components to each other and to standard drugs. Flavones induce relaxation of the carbachol contracted tracheal strip without stimulation of the beta 2-receptors, which were blocked by propranolol.