Some investigators have hypothesized that estrogens and other hormonally active agents found in the environment might be involved in breast cancer increases and sperm count declines in humans as well as deformities and reproductive problems seen in wildlife. This book looks in detail at the science behing the ominous prospect of 'estrogen mimics' threatening health and well-being, from the level of ecosystems and populations to individual people and animals. The committee identifies research needs and offers specific recommendations to decisionmakers. This authoritative volume critical evaluates the literature on hormonally active agents in the environment and identifies known and suspected toxicologic mechanisms and effects of fish, wildlife, and humans. The book examines whether and how exposure to hormonally active agents occurs--in diet, in pharmaceuticals, from industrial releases into the enviornment--and why the debate centers on estrogens and identifies significant uncertainties, limitations of knowledge, and weakensses in the scientific literature.