The recent cases of anthrax due to bioterrorism in the United States have reminded us that our society is also vulnerable to biological attacks. Illnesses due to bioterrorism are not naturally occurring diseases, and therefore may show presentations not familiar to many doctors. The last case of smallpox was reported in 1960, and doctors aged less than 60 years have no experience of smallpox. Anthrax is a rare zoonosis, and no case of inhalation anthrax has been reported in Korea. American doctors might be on high alert to bioterrorism after September 11, 2001. However, it took more than 2 weeks from the symptom onset of the index case to the recognition that anthrax outbreak had occurred due to bioterrorism. This delay shows how difficult it is to recognize bioterrorism. This article describes clinical recognition and management of patients exposed to biological warfare agents, especially agents causing anthrax, smallpox, plague, and botulism.