Anthrax, a disease of animals and humans, is caused by an aerobic, spore-forming, Gram-positive rod—Bacillus anthracis. Some of the more common synonyms are charbon, malignant pustule, malignant carbuncle, milzbrand, splenic fever, and woolsorter’s disease. Anthrax bacilli that lose the ability to produce capsules do not cause disease. This fact has played an important role in the development of a safe and effective live avirulent vaccine. Polyglutamic acid extracts from anthrax bacilli have been shown to be virtually nontoxic and inert when injected into animal tissues. Anthrax occurs in animals in at least three different forms: peracute or apoplectic, acute, and subacute to chronic. The pathogenic sequence of anthrax has been followed in artificially infected laboratory animals exposed to virulent spores. A significant number of anthrax cases that occur in livestock are prediagnosed or highly suspected by the veterinarian or laboratory personnel when clinical specimens are submitted, often with detailed histories and necropsy lesions.