Fifty-two-week oral toxicity and 24-week intramuscular toxicity of a new synthetized biliary acid, taurohyodeoxycholic acid (Io, Praxis, CAS 2958-04-5) were investigated in dogs. Taurohyodeoxycholic acid was orally administered at dose levels up to 500 mg/kg/d and i.m. administered at dose levels up to 200 mg/kg/d. No deviations from normality were observed in mortality, physical appearance and general behaviour of the treated animals. Food and water consumption and body weight gain of treated groups did not differ from those of control animals. No treatment-related changes were observed in hematology, serum biochemistry, urinalysis, organ weights and post-mortem macroscopic or histopathological examinations. No dose- or sex-related differences were observed. The no-effect dose level was estimated to be 500 mg/kg/d in the chronic oral toxicity study and 200 mg/kg/d in the intramuscular study.