Phytoestrogenic substances have previously been isolated and identified in two alcoholic beverages: bourbon and beer. To delineate the relative potencies of the estrogenic substances of plant origin thus far identified in these commonly consumed alcoholic beverages, we evaluated the ability of biochanin A, beta-sitosterol, genistein, and daidzein to bind to cytosolic estrogen receptor binding sites. The in vitro studies demonstrated that each of the contained substances was capable of effectively competing for cytosolic estrogen receptor binding sites of rat liver and uterus. Further, the two phytoestrogenic constituents of bourbon, beta-sitosterol and biochanin A, were less potent than those present in beer. Given the high concentration of beta-sitosterol in bourbon, we chose to evaluate the estrogenicity of beta-sitosterol in vivo using ovariectomized rats. beta-sitosterol was administered either daily or intermittently at 3 doses, based on amounts previously determined to be present in bourbon. The in vivo studies demonstrated that beta-sitosterol is capable of producing a weak estrogenic effect only at the lowest dose (6.2 micrograms/dl) administered intermittently. These responses suggest that beta-sitosterol may be weakly estrogenic at low doses, but is unable to maintain such an effect at higher doses.