On September 11, 2001, following the terrorist incidents in New York City and Washington, D.C., CDC recommended heightened surveillance for any unusual disease occurrence or increased numbers of illnesses that might be associated with the terrorist attacks. Subsequently, cases of anthrax in Florida and New York City have demonstrated the risks associated with intentional release of biologic agents. This report provides guidance for health-care providers and public health personnel about recognizing illnesses or patterns of illnessthat might be associated with intentional release of biologic agents.