In order to characterize changes in bile acid profile during liver cell damage and regeneration, levels of bile acids in serum and bile were determined by high performance liquid chromatography (HPLC) in F344 rats treated with a single dose of D-galactosamine (galactosamine, 300 mg/kg, i.p.) or subjected to two-thirds partial hepatectomy (PH). In the serum, galactosamine caused elevation of conjugated bile acids such as taurocholic acid (TCA) and tauro-beta-muricholic acid (T beta MCA) at the 24 and 48-h time points, whereas unconjugated bile acids including cholic acid (CA) at 24 h and hyodeoxycholic acid (HDCA) at 48 h were increased after PH. In the bile, elevation of TCA showed most remarkable elevation at the 24-h time point in the galactosamine-treated group. All components of biliary bile acids showed rapid decreases from 24 to 48 h. The results demonstrated that while liver tissue damaged by galactosamine is able to conjugate bile acids it allows leakage into the blood stream. In contrast, the results for rats subjected to PH indicated that liver cells during DNA synthesis are not capable of conjugating all free bile acids with taurine although a similar leakage occurs. It is concluded that obvious elevation of serum TCA or CA and biliary T beta MCA could be a useful indicator of hepatocellular proliferation.