The effects of taurine feeding on plasma cholesterol concentrations and fecal bile acid excretion were examined in young and aged male and female rats (5 weeks and 10 months old respectively), the latter either ovariectomized (ovx) or sham-operated. The rats were fed a cholesterol-free diet (C diet) or a cholesterol-free taurine-supplemented diet (T diet; C + 5% taurine) for 28 days. In males, plasma cholesterol concentrations and fecal bile acid excretion were higher and lower, respectively, in aged rats than in young rats, but were not affected by feeding with the T diet. In female rats, plasma cholesterol concentrations were higher in aged rats than in young rats and higher in ovx-rats than in sham-operated rats. In contrast to male rats, plasma cholesterol concentrations were lower in female rats fed the T diet than in those fed the C diet. Plasma cholesterol concentrations were increased in aged ovx-rats, but decreased by feeding with the T diet. Fecal bile acid excretion was higher in rats fed the T diet than in those fed the C diet. Thus, these data indicate that the hypocholesterolemic effect of taurine is greater in aged rats than in young rats.