The present investigation was conducted to study the effect of 2'-[2-(diethylamino)ethoxy]-3-phenylpropiophenone hydrochloride (etafenone hydrochloride) on the action of various bronchoactive agents using isolated guinea pig tracheal tissues. Acetylcholine hydrochloride, prostaglandin F2a, histamine dihydrochloride and serotonin-creatinine sulfate induced contractile responses in guinea pig tracheal tissues were attenuated, while, isoprenaline hydrochloride, prostaglandin E2, salbutamol hemisulfate, aminophylline and adrenaline-induced relaxing responses were potentiated with continuous infusion of etafenone hydrochloride. These results suggest that etafenone hydrochloride would become a useful therapeutic agent in the treatment of chronic obstructive pulmonary disease.