Three groups of golden Syrian hamsters were fed equimolar amounts of taurine-conjugated ursodeoxycholic acid (TUDCA) or unconjugated ursodeoxycholic acid (UDCA) with or without excess taurine for 2 wk. They also received a lithogenic diet composed of standard rodent chow containing ethynylestradiol and increased cholesterol. Bile was obtained from the gallbladder after ketamine anesthesia and analyzed for biliary lipids. The percentage of biliary UDCA was higher with TUDCA (38.5 +/- 3.7) than with UDCA plus taurine (26.5 +/- 2.0, P less than 0.01). The glycine-to-taurine ratio of biliary UDCA conjugates was lower with TUDCA (0.9 +/- 0.1) than with UDCA plus taurine (2.1 +/- 0.2, P less than 0.01) and was highest with UDCA without taurine (4.1 +/- 0.1, P less than 0.01). Biliary cholesterol (molar percentage) and the cholesterol saturation indices with or without correction for UDCA-rich bile were significantly lower with TUDCA than with unconjugated UDCA with or without added taurine. In conclusion, administration for 2 wk of TUDCA, compared with an equimolar amount of unconjugated UDCA plus taurine, produced in the bile of hamsters a higher percentage of UDCA, a lower glycine-to-taurine ratio of UDCA conjugates, and a lower saturation index before and after adjustment for UDCA-rich bile.