Two lignin-degrading basidiomycetes, Stereum hirsutum and Heterobasidium insulare, were used to degrade bisphenol A (BPA) in culture, and the estrogenic activity of the degradation products was examined using MCF-7 cell proliferation assays (E-screen) and analysis of pS2 mRNA expression in MCF 7 cells. Both S. hirsutum and H. insulare showed high resistance to BPA 100 ppm, and their mycelial growth was fully completed within 8 d of incubation at 30 degrees C. It took 7 to 14 d to achieve complete degradation (ca. 99%) of BPA by both fungi. MCF-7 cells proliferated actively at a BPA concentration of 10(-5) M. However, cell line proliferation was significantly inhibited when the cells were incubated in BPA culture media containing S. hirsutum and H. insulare. Similar results were obtained regarding pS2 mRNA expression. The pS2 mRNA expression levels decreased by 1.5-fold in supernatant from BPA treated with S. hirsutum and H. insulare compared with those treated with BPA alone.