Facilities handling large amounts of potentially hazardous chemicals (i.e., chemical facilities) might be of interest to terrorists, either as targets for direct attacks meant to release chemicals into the community or as a source of chemicals for use elsewhere. Because few terrorist attacks have been attempted against chemical facilities in the United States, the risk of death and injury in the near future is estimated to be low, relative to the likelihood of accidents at such facilities or attacks on other targets using conventional weapons. For any individual facility, the risk is very small, but risks may be increasing with potentially severe consequences for human health and the environment. Available evidence indicates that many chemical facilities may lack adequate safeguards.