A comprehensive data base of chemicals identified in human biological media has been established under the direction of the Exposure Evaluation Division in the US Environmental Protection Agency's Office of Toxic Substances. This centralized resource of body-burden information has grown out of the concern of government scientists over continuing reports of toxic chemicals in human tissues and body fluids. Body burden is a reflection of exposures to food, air, and water contaminants, as well as administration of pharmaceuticals. The systematic acquisition of body-burden data will facilitate a more relevant assessment of human exposure to xenobiotics than was previously possible using environmental contamination levels. Data were obtained primarily from the open literature (retrospective to 1974), and contains information on over 950 different substances. For the user's convenience, cross-referenced chemical lists of CAS preferred names and common names are provided. The human tissues and body fluids found to be contaminated by these chemicals are also listed. The data base is published annually in tabular format with indices and chemical listings that allow specific searching. The file is now available online in the US Department of Energy's RECON and is being prepared for Lockheed's DIALOG. The purpose of the data base is to provide a centralized resource of body-burden data. (ERA citation 08:016379)