Estrogens are represented by a diverse group of compounds. Within this large family of molecules are tissue-selective estrogens that have been classified as selective estrogen receptor modulators (SERMs). These compounds are characterized by the fact that they exhibit both estrogen agonist and antagonist activity dependent upon the gene promoter and target tissue being examined. SERMs have been intensively studied over the past decade, especially since one, raloxifene, has been approved for the prevention and treatment of postmenopausal osteoporosis. While not a replacement for hormone replacement therapy (HRT), raloxifene can be an alternative to it and other treatments for osteoporosis. The ideal SERM would provide the positive benefits associated with HRT without the uterine and breast stimulation. Raloxifene does achieve some of the benefits of HRT, specifically on the skeleton and lipid metabolism with no apparent uterine effects, and a potential decreased risk of developing breast cancer associated with raloxifene therapy. However, there are a number of parameters that can be improved. A number of SERMs have been evaluated only to fail in development due to, for the most part, uterine safety issues. In order to develop an improved SERM, a stringent screening process was designed to select compounds that did not stimulate the uterus or breast. At the same time, these new compounds would have a positive impact on the skeleton and lipid metabolism with the additional improvement (over raloxifene) of a neutral effect on hot flashes. Under these strict conditions, WAY-140424 was developed and, to date, the preclinical pharmacology data have accurately predicted the clinical response demonstrated in phase I and II trials.