There are many subclones of human breast cancer MCF-7 cells that respond to different degrees of estrogen and that have been used for testing the estrogenic activity of environmental chemicals such as bisphenol A. Here, we examined the estrogenicity of bisphenol A in an MCF-7 subclone. It was not able to detect the increment of BrdU incorporation by neither 10^-7 M bisphenol A alone nor 10 ng/mL epidermal growth factor (EGF) alone in the cells (1 x 10⁴ cells) up to 50 hr. However, in the presence of 10 ng/mL EGF, bisphenol A dramatically increased cell proliferation (ED₅₀ = 10 pM). The synergistic responses were the chemical concentration-dependent manner. Thus, in this study, we demonstrate the new insight into the action of bisphenol A in the MCF-7 subclonal cell.