The recognition of selective estrogen receptor modulation in the mid-1980s provided a unique opportunity to develop multifunctional drugs. Tamoxifen, the first selective estrogen receptor modulator (SERM), is the first antiestrogen to be tested successfully for the prevention of breast cancer in high-risk women. However, the recognition that SERMs maintain bone density and lower circulating cholesterol suggested that the prevention of osteoporosis and coronary heart disease would be beneficial side effects of tamoxifen treatment. This hypothesis has not been pursued in clinical trial, but an alternate hypothesis, that SERMs could be developed to prevent osteoporosis and potentially reduce the risk of breast cancer, has been pursued with raloxifene. Current molecule modeling of the SERM-ER complex has identified the reason for the promiscuous estrogen-like actions of tamoxifen compared with raloxifene. Future studies of the signal transduction pathways of the ER alpha (alpha)- and beta (beta)-SERM complexes hold the promise of new drug discoveries and a menu of preventive medicine in clinical practice.