The role of androgens and the androgen receptor (AR) in the development and progression of breast cancer is poorly understood. To further define a potential model for androgen action in breast cancer, MDA-MB-453 cells, which express AR in the absence of oestrogen receptors and progesterone receptors, were further characterised in terms of AR expression and androgen responsiveness. High level expression of AR was confirmed by northern blot analysis, radioligand binding and immunocytochemistry, and could not be accounted for by AR gene amplification. Three endogenous androgen-responsive genes (fatty acid synthetase, gross cystic disease fluid protein of 15 kDa and prolactin receptor) and a transfected reporter gene, containing an androgen-responsive element, were induced following androgen administration. A synthetic androgen, mibolerone, induced moderate (27% above control) stimulation of MDA-MB-453 cell proliferation, which was abrogated by the simultaneous administration of the synthetic androgen antagonist, anandron, demonstrating that the effect was AR-mediated. In summary, MDA-MB-453 cells express high levels of functional AR, and thus provide a valuable in vitro model for further studies on androgen regulation of gene expression, and perhaps cell proliferation in breast cancer.