Sexual steroid hormones, androgens and oestrogens, are significant factors for the maintenance of the quality of bones, and their decline in old age may participate in the development of osteoporosis. The marked variability of the effect of oestrogenic substances in different tissues led to the development of new substances which should have these oestrogenic properties different from natural oestrogens. They should have a positive effect on bone and the cardiovascular system without affecting the organs of reproduction. With regard to comparison of effects of this group of substances at the level of oestrogen receptors in different organs they may be included in the group of selective modulators of oestrogen receptors (SERM). Representatives of these substances com- prise tamoxifen, commonly used in the treatment of breast tumours, and raloxifen used in the treatment of postmenopausal osteoporosis. It is assumed that further advances at the level of molecular biology of oestrogen receptors will lead to a further extension and classification of SERM.

        Key words: osteoporosis, oestrogen, tamoxifen, raloxifen