Environmental chemicals with inherent estrogenic activity are supposed to be responsible for the decrease of quantity and quality of human sperms during the past 40 years. The current hypothesis is that estrogenic agents acting during fetal life may lead to impaired development of the testes and of the male reproductive tract in the human as well as in several wildlife species. However, from clinical and experimental data it is known, that estrogens may also lead to impairment of female reproductive functions. Perinatal application of DDT, octylphenol and benzylbutylphthalate resulted in persistent estrus in rats, in- and subfertility, respectively, and impaired sexual behaviour. Epidemiological and experimental data speak in favour of environmental estrogens to be one cause for the development of polycystic ovaries, being the most important reason for female infertility in the human.