To evaluate the estrogenic activities of several chemicals such as 17beta-estradiol (E2), rho-nonylphenol, bisphenol A, butylparaben, and combinations of these chemicals, we used recombinant yeasts containing the human estrogen receptor [Saccharomyces cerevisiae ER + LYS 8127]. We evaluated E2 was most active in the recombinant yeast assay, followed by rho-nonylphenol, bisphenol A, butylparaben. The combinations of some concentrations of 17-estradiol as a strong estrogen and bisphenol A or butylparaben as a weak estrogen showed additive estrogenic effects. Also, the combinations of some concentrations of nonlyphenol and butylparaben and combination of butylparaben and bisphenol A showed additive effects in the estrogenic activity. Therefore, the estrogenic activities of the combinations of two chemicals were additive, not synergistic.