Soy isoflavone's (genistein and daidzein in particular) biological significance has been thoroughly studied for decades, so we started from the premise that refreshed investigation approach in this field should consider identification of their new molecular targets. In addition to recently described epigenetic aspects of polyphenole action, the cell membrane constituents-mediated effects of soy isoflavones are worthy of special attention. Accordingly, the expanding concept of membrane steroid receptors and rapid signaling from the cell surface may include the prominent role of these steroid-like compounds. It was observed that daidzein strongly interacts with membrane estrogen receptors in adrenal medullary cells. At low doses, daidzein was found to stimulate catecholamine synthesis through extracellular signal-regulated kinase 1/2 or protein kinase A pathways, but at high doses, it inhibited catecholamine synthesis and secretion induced by acetylcholine. Keeping in mind that catecholamine excess can contribute to the cardiovascular pathologies and that catecholamine lack may lead to depression, daidzein application promises to have a wide range of therapeutic effects. On the other hand, it was shown in vitro that genistein inhibits LNCaP prostate cancer cells invasiveness by decreasing the membrane fluidity along with immobilization of the androgen receptor containing membrane lipid rafts, with down regulation of the androgen receptors and Akt signaling. These data are promising in development of the molecular pharmacotherapy pertinent to balanced soy isoflavone treatment of cardiovascular, psychiatric, and steroid-related malignant diseases.