By Congressional mandate, the Agency for Toxic Substances and Disease Registry (ATSDR) produces "toxicological profiles" for hazardous substances found at National Priorities List (NPL) sites. These hazardous substances are ranked based on frequency of occurrence at NPL sites, toxicity, and potential for human exposure. Toxicological profiles are developed from a priority list of 275 substances. ATSDR also prepares toxicological profiles for the Department of Defense (DOD) and the Department of Energy (DOE) on substances related to federal sites. So far, 296 toxicological profiles have been published or are under development as “finals” or “drafts for public comment”; 281 profiles were published as finals; 130 profiles have been updated. Currently, 7 profiles are being revised based on public comments received. These profiles cover more than 250 substances.