Effects of 1-methyl-3,3-diphenyl-1N-tert.-butyl-propylamine-hydrochloride (terodilin, Bicor) on bronchial muscle and mucociliary function was studie in isolated airways preparations of rats. Terodilin blocked the bronchoconstrictor effect of acetylcholine but was ineffective against that caused by serotonin and bradykinin. The alteration of the dose-respone curves of acetylcholine by terodilin indicated that terodilin is a partial agonist of acetylcholine with a very small intrinsic activity. This finding may explain the ciliostimulatory effect of this drug.