Book excerpt: Studying animals in the environment may be a realistic and highly beneficial approach to identifying unknown chemical contaminants before they cause human harm. Animals as Sentinels of Environmental Health Hazards presents an overview of animal-monitoring programs, including detailed case studies of how animal health problemsâ€"such as the effects of DDT on wild bird populationsâ€"have led researchers to the sources of human health hazards. The authors examine the components and characteristics required for an effective animal-monitoring program, and they evaluate numerous existing programs, including in situ research, where an animal is placed in a natural setting for monitoring purposes.