The metabolites of diltiazem in the urine of rats, dogs and man and rat bile were investigated. New metabolites including six acidic metabolites (A1-A6) and four basic metabolites (M9, MB, MC, MD) were isolated by high performance liquid chromatography and their structures were characterized by gas chromatography-mass spectrometry. Acidic metabolites A1, A2, A3, A4 and basic metabolite MD identified by comparing their properties with the synthetic compounds ; (+)-(2S, 3S)-2-(4-methoxyphenyl)-3-acetoxy-4-oxo-2, 3, 4, 5-tetrahydro-1, 5-benzothiazepin-5-acetic acid (A1), 3-deacetyl-A1 (A2), O-demethyl-A1 (A3), O-demethyl-3-deacetyl-A1 (A4) and N-didemethyl-diltiazem (MD). All acidic metabolites have a CH2COOH group which may be formed by oxidative deamination of the CH2CH2N (CH3)2 group of diltiazem.