The presence of estrogens in the male gonad is now well documented, however the role of the hormones in regulation of function of male reproductive system is not fully understood. The using of molecular biology methods provided evidence that the cells of male reproductive system organs are able to produce estrogens via aromatization of androgens and are estrogen target. The cytochrome P450 aromatase and both isoform of estrogen receptors are expressed not only in Leydig and Sertoli cells, but also in germ cells, spermatozoa, the cells of epithelium in the efferent ductules and epididymis.

There are many hypotheses on the increase of male infertility. The phenomenon is believed to be connected with the presence of substances with hormonal activity – xenoestrogens in human environ- ment. The substances are divided into two groups: man made substances and components occurring naturally – phytoestrogens. Steroids influence not only male and female reproductive systems but also development and function of another tissue. Therefore, this is very important to list of substances with hormonal activity, their potency of acting, the way of expositions.