A variety of substances are now known to disrupt the hormonal balance of an organism. The connection between the disturbances observed and pollution with xenoestrogens (endocrine disrupting chemicals, EDCs) has been demonstrated in some wildlife populations and has been hypothesised in humans. The present report documents the current situation and reviews the state of knowledge and data available for Switzerland. An evaluation of environmental pollution by selected chemicals is given. The research requirement is deduced from the gaps in knowledge identified, which must be closed in order for the situation to be assessed more precisely. There is a significant need for further research both into pollution itself and its disruptive effects. Further studies currently in progress in Switzerland are summarised.