A study of the metabolism of 3-methylcholanthrene (3-MC) injected i.v. into mice has shown that the metabolites excreted in the bile could be separated into six subfractions, FIII-1, FIII-2, and FIV-1 to -4, by combined chromatography on a Sephadex LH-20 column and on a thin layer of silica gel. These metabolites were water soluble and were considered to be conjugates of mono- or dihydroxy-3-MC with glucuronic or sulfuric acid. These water-soluble conjugates were freed from the acids in the cecum and large intestine and were converted into ether-soluble substances, FI and FII, which consisted of 10 and 4 subfractions, respectively. Among the subfractions of FI, cis- and trans-1,2-dihydroxy-3-MC, 2-hydroxy-3-MC, 2-keto-3-MC, and intact 3-MC were detected. FII subfractions were considered to be metabolites of 3-MC oxidized at positions 4 to 10. 11,12-Dihydro-11,12-dihydroxy-3-MC, the so-called K-region dihydro diol, was not detected in the subfractions of FI and FII. However, a further oxidized metabolite of this dihydro diol may appear in one of the FI subfactions. Fraction FV and FV′, appearing in contents of the intestine, were intermediate substances from the conjugated metabolites to FI and FII subfractions.