Hydrazines are colorless liquid compounds that have been found at various Department of Defense hazardous waste sites. They are designated as environmental contaminants causing adverse effects to public health and have been identified at many National Priorities List (NPL) hazardous waste sites and federal facilities sites in the United States. Three chemically similar hydrazines-hydrazine, 1,1-dimethylhydrazine, and 1,2-dimethylhydrazine--occur in the environment and cause adverse health effects to persons living near hazardous waste sites. Humans are exposed to hydrazines by drinking contaminated, water, by inhaling contaminated air, or by swallowing or touching contaminated dust. Human occupational data and studies in laboratory animals suggest that people exposed to hydrazines may develop adverse systemic health effects or cancer. Hydrazines have caused cancer in animals following acute- or intermediate- duration exposure by the oral and inhalation routes. The U.S. Environmental Protection Agency, the U.S. Department of Health and Human Services, the International Agency for Research on Cancer, and the World Health Organization have classified hydrazines as possible cancer-causing environmental contaminants.