To investigate the effects of conjugated bile acid on bacterial growth and cholylglycine hydrolase activity, Clostridium perfringens from human feces was exposed to varying concentrations of taurine- or glycine-conjugated chenodeoxycholic acid. Extracellular enzyme activity was determined by deconjugation of radiolabeled taurocholic acid and viable cells were counted after anaerobic culture at 37 degrees C for 24 h. Viable cells were decreased with more than 1.0 mg of conjugated chenodeoxycholic acid per mL and there were no viable cells with 10.0 mg of bile acid per mL. Although total enzyme activity was decreased according to the bile acid concentration, enzyme activity per bacterium was increased between 1.0 and 4.0 mg/mL. There were no statistically significant differences between the types of conjugation. It was concluded that conjugated bile acids may exert inhibitory effect on bacterial growth and extracellular cholylglycine hydrolase activity in Clostridium perfringens. However, under the physiologic condition in the human intestine, conjugated bile acid might induce production of extracellular cholyglycine hydrolase per bacterium.