Bacillus anthracis causes anthrax in all mammals, including humans. Depending upon the route of entry of B. anthracis spores, infection can result in cutaneous lesions, which are readily treatable with antibiotics, or systemic lethal disease, which is nearly always fatal. The continuing worldwide incidence of anthrax in animal populations, the risk of human infection associated with animal outbreaks, and the threat of use of B. anthracis as a biological weapon warrant continued investigation of this organisms and its virulence mechanims. Furthermore, B. anthracis is an excellent model system for inverstigation of virulence gene expression by bacteria.