Inhalational anthrax is caused by the entry of Bacillus anthracis spores into the lung. Inhaled spores are phagocytosed by alveolar macrophages. Bacilli then escape from the macrophage and spread to other cells, initiating a systemic anthrax infection. Based on the pathological studies of primate and human inhalational anthrax cases, it appears that lung tissue injury is a lethal consequence of the disease. Although the cytotoxicity of anthrax lethal toxin to macrophages is well known, it is not clear how anthrax toxin affects the various lung cell types.