Objectives are: To confirm the safety and tolerability of 2-dose regimens of 100 g rPA vaccines (3 products) administered by the intramuscular (IM) route to healthy adults.To describe the immunologic responses to 2-dose regimens of 3 rPA vaccines and to compare the responses to those following administration of Anthrax Vaccine Adsorbed (AVA or BioThraxTM), the currently available vaccine. The primary immunologic outcome is the proportion of volunteers in each group that mounts an antibody response (defined as a 4-fold or greater increase from pre-vaccination to post-vaccination of anti-rPA IgG antibody with a minimal concentration of 10 µg/ml as measured by ELISA). Secondary outcomes are time to peak response and GMC of anti-PA antibody at peak for each group. In addition, the following immunologic assays will be performed: toxin neutralization assay, oral fluid ELISA, antibody avidity, IgG subclasses, and B-cell memory,T-cell memory and effector subpopulations.