 The intentional use of Bacillus anthracis in 2001 as a bioterrorism weapon with fatal consequences renewed interest in past epidemiologic and animal research about pathogenesis and posed new dilemmas about diagnosis and treatment. Cases in the October 2001 US outbreak were theoretically exposed via one dispersal method: aerosolization of Ames strain spores. While some developed the cutaneous anthrax form, others sustained the more serious inhalational disease. Inhaled spores are known to travel to alveolar macrophages and then onto the mediastinal lymph nodes where germination to the bacterium form and toxin release are thought to occur. Infective dose, significance of dormant spores after long-term antibiotic therapy, spectrum of disease and even precise cause of death remain unknown. This observational, prospective natural history study was developed during the 2001 outbreak and is set up to follow participants from the time of exposure through post-recovery greater than ten years. Healthy vaccinated participants have been included to evaluate serum titers and cell markers in relation to dose and frequency of AVA vaccine. 