Long-term environmental effects of chemical exposure have long been of concern and chemicals which cause changes to the sexual development of exposed organisms have now been identified. It is thought that low-level exposure to a wide range of chemicals may be affecting endocrine function, leading to a reduction in fertility and an increase in reproductive cancers. This is a review of the scientific evidence, attempting to put the subject into context. Along with an overview of the issue, there is discussion of the specialized aspects in relation to wildlife; environmental oestrogens and male reproduction; and naturally occurring oestrogenic substances. With contributions from representatives of the Medical Research Council's Institute for Environment and Health and the US Environmental Protection Agency, the articles provide a comprehensive review of current issues.