After [24-14C]delta 6-lithocholic acid was injected into the cecum of rats, [14C]lithocholic acid was identified as a metabolite in feces. When the labeled delta 6-bile acid was injected intraperitoneally into bile-fistula rats, radioactivity excreted in bile was contained most abundantly in the taurine-conjugated fraction of bile acids. In the fraction, taurine conjugate of [14C]delta 6-lithocholic acid but of neither [14C]lithocholic acid nor other bile acids was found. The results showed that [24-14C]delta 6-lithocholic acid was reduced to [14C]lithocholic acid by the intestinal flora but not by the liver, which, however, was capable of conjugating delta 6-lithocholic acid with taurine.