Plague is a disease that has been present for thousands of years and described since the earliest medical accounts. It occurs today worldwide, and may present in a variety of clinical forms. Bubonic disease, pneumonic plague, and septicemic plague are seen in addition to a number of other less common manifestations. As an agent of bioterrorism,Yersinia pestis could pose an extreme threat if released in the appropriate form and in the appropriate environment. Presumptive diagnosis may be made with readily available techniques, but laboratory handling of specimens requires special care. When there is a strong suspicion of plague, treatment should be instituted immediately, as delaying therapy will result in increased morbidity and mortality.