The ability of the biliary metabolite retinotaurine to reverse the cornification of vaginal epithelial cells induced by vitamin A deficiency was assessed using a vaginal smear assay. Retinotaurine activity was examined following the intravaginal administration of 10(-12) mol to 10(-8) mol of this compound per vagina. This metabolite exhibited no detectable activity at any dose tested. These results show that retinotaurine cannot be more than 1% as active as all-trans-retinoic acid since retinoic acid shows a response at concentrations of 10(-10) mol per vagina. The low biological activity of this recently identified biliary metabolite suggests that it represents an excretory form of retinoic acid.