Endocrine disruptors and their possible impact on human and animal health have become a topic of discussion and an area of active research in toxicology. A focus has been on xenoestrogens, i.e., environmental chemicals with estrogenic activity. In principle, there is agreement that such compounds, in high doses, may cause developmental, reproductive and tumorigenic effects ("hazard"). A matter of controversy is the question of risks associated with xenoestrogens under realistic (low) exposure scenarios; this is due to uncertainty on how to assess the interactions of exogenous compounds with the endocrine system and its complex regulation. Our overview will address topics including: consequences from previous clinical use of the potent estrogen diethylstilbestrol with particular emphasis on dose-response relationships, other observations in humans exposed to estrogenic chemicals in an occupational context, and available information on exposure levels of synthetic and naturally occurring estrogens in the diet. Together with a critical appraisal of methods to detect and quantitate the estrogenic activity of synthetic and naturally occurring chemicals, novel aspects in the risk assessment for endocrine active compounds are discussed.