Terrorism has become an undeniable reality in the United States today. In addition to conventional weapons, there is increasing concern that criminal individuals, terrorist groups, or nations may resort to the use of biological, chemical, or radiological weapons. There is a long history of use of biological and chemical weapons on the battlefield. While these weapons have been used on occasion in the United States, the events of September 11, 2001 and the anthrax mailings of October 2001 have made the potential danger evident. Physicians, nurses, first responders and other health care personnel in American cities can no longer afford to be uninformed about biological, chemical and radiological weapons. Rapid recognition of a clinical syndrome consistent with a bioterrorist agent will facilitate not only appropriate early treatment of the victim, but will give public health officials time to conduct a rapid epidemiologic investigation to identify other exposed individuals and deliver appropriate prophylactic measures to prevent or ameliorate disease. For many biological weapons, a narrow window of opportunity exists during which a prophylactic measure can be administered to prevent or treat disease. Delay in recognition will cost lives. Delayed recognition of contagious bioterrorist agents, chemical agents, and radiological contamination will harm the affected patients by depriving them of the necessary appropriate treatment or decontamination and lead to infection or contamination of health care workers.