A high intake of isoflavones is associated with a reduction of breast cancer among Japanese women. The aim of this study was to quantify BRCA2 tumor suppressor gene expression after treatment of cells with the phytoestrogens daidzein and genistein, the main compounds of soy. The effects of 5 microg/ml genistein and 20 microg/ml daidzein on BRCA2 expression were studied in two human mammary tumor cell lines, MCF7 and MDA-MB-231, and one normal human breast epithelial cell line, MCF10a. BRCA2 mRNA was evaluated by quantitative real time RT-PCR and the amount of BRCA2 protein was measured by affinity chromatography. With Genistein, we observed a 60% increase of BRCA2 mRNA in MDA-MB-231 and MCF10a, which are, respectively, estrogen receptors alpha-/beta+ and alpha-/beta-, and no variation in MCF7, which is ERalpha+/beta+. Dairzein had no effect on BRCA2 mRNA expression. The level of BRCA2 protein with both food components also remained unchanged in all three cell lines. This suggests regulation of BRCA2 between the mRNA and protein levels. Treatment with actinomycin D and cycloheximide demonstrated that the increase in BRCA2 mRNA was not blocked by cycloheximide, indicating that de novo protein synthesis was required in MDA-MB-23, although de novo synthesis was not required in MCF10a for the genistein. With actinomycin D, genistein had a positive effect on the transcriptional level of BRCA2 mRNA in MDA-MB-231 and MCF10a. The use of an anti-estrogen suggested that the action of daidzein and genistein might not be mediated through the ER.