It has become clear in recent months that the threat of bioterrorism is very real. All physicians need to be aware of the presenting signs and symptoms of the most likely agents. Allergists and immunologists care for a unique population of patients with several alterations of their immune system that might change the expected course of illnesses from biologic terror agents. In this review, we discuss specific bioterrorism agents, focusing on their presentation, pathogenesis, and immunology. In addition, we describe how these illnesses might differ in the population of patients followed by allergists and immunologists. (J Allergy Clin Immunol 2002;109:214-28.)