The metabolic fate of ο-chloro-α-(tert-butylaminomethyl)-benzyl alcohol hydrochloride (C-78) in the rat was studied by oral administration of ¹⁴C-C-78, and the bronchodilating activities of the metabolites were also examined. The major metabolites in the urine, bile, and feces were unchanged C-78 (I) and 4-hydroxy- (II), 3-hydroxy- (III), and 4-hydroxy-5-methoxy-C-78 (IV), and their corresponding conjugates. As the minor metabolites, ο-chlorobenzoic acid, ο-chloromandelic acid, and 1-(ο-Chlorophenyl)-1, 2-ethanediol were detected by gas chromatography. These results suggested that the major metabolic pathway of C-78 in the rat is hydroxylation of the benzene ring. Although IV had no activity, II had a stronger bronchodilating activity than C-78, and III was as effective as C-78, suggesting the participation of the metabolites in the bronchodilating action and durability of C-78.