In the discussion of the risk-benefit relation of the hormone replacement therapy (HRT) for elder women phytochemicals with estrogenic activity received a great deal of attention. Phytoestrogens are naturally occurring compounds with structural similarity to 17beta-estradiol. Especially genistein, an isoflavone most abundant in soy, possess a high and selective binding-affinity to the mammalian estrogen receptors. It has been found, that genistein exert in humans both: weak estrogenic and anti-estrogenic effects, similar to the SERMs. Consequently, it was concluded, that genistein might provide an alternative to prevent postmenopausal bone-loss and ameliorate menopausal symptoms without side-effects similar to HRT. Pre-clinical experiments and results from clinical pilot studies with pure genistein confirmed its efficacy in these indications. Nevertheless, currently some open issues still exist to recommend its intake thoughtlessly. Bonistein, pure synthetic genistein developed by DSM Nutritional Products, was tested extensively in appropriate models for bone health. A battery of toxicological studies was conducted to determine safe intake levels. In the early clinical development pharmacokinetic studies were performed in healthy volunteers and in postmenopausal women. Now large-scale studies are in preparation to investigate Bonistein's efficacy in postmenopausal bone-loss and climacteric syndrome.