The E-CALUX assay has been established to measure the estrogenic activity of agents such as exogenous endocrine disrupting chemicals. The method utilizes human ovarian carcinoma cells, and is able to evaluate estrogenic activity as a reporter gene assay by using estrogen receptors (ERs) expressed endogenously. However, we have no information about the subtypes of ERs that ovarian carcinoma cells express. Therefore we detected the expression of both ER-αand ER-β by RTPCR, and determined the ratio of ER-α to ER-β to be 5.7: 1 using semi-quantitative real-time PCR. Further, the protein expression of each ER subtype was detected using immunocytochemistry. These results suggest that estrogenic activity detected with the E-CALUX assay is mainly ER-α dominant and the additive estrogenic activity was observed when cells were stimulated with the combination of 17βestradiol (E2) and pesticides (pyriproxyfen, thiabendazole (TBZ) and ο-phenylphenol (OPP)), respectively.