['The aim of the present study was to identify the mechanism by which genistein and 17β-estradiol inhibit proliferation of MDA-MB-231 breast cancer cells.', 'The expression of cell signaling proteins involved in cell apoptosis, proliferation, and survival (BCL-2 associated X protein, BAX; B-cell lymphoma 2, BCL-2; extracellular signal regulated kinase, pERK1/2; and protein kinase B, pAKT) were examined by western blotting, and tested whether these effects correlated with cell proliferation and apoptosis.', 'Compared to the control, 1 μM genistein plus 1 nM 17β-estradiol significantly increased apoptosis, and the BAX/BCL-2 ratio, with a concomitant decrease in ERK1/2 phosphorylation. High concentrations of genistein (100 μM) both in the presence and absence of 17β-estradiol also increased apoptosis; however, these changes were not correlated with the BAX/BCL-2 ratio or with phosphorylation of ERK1/2.'] Do physiological concentrations of genistein and 17β-estradiol inhibit MDA-MB-231 breast cancer cell growth by increasing BAX/BCL-2 and reducing pERK1/2?