Anthrax CVD 3000: A Phase II Study to Assess the Safety, Tolerability, Immunogenicity, and Optimal Primary Schedule of 3 Recombinant Protective Antigen (rPA) Anthrax Vaccines Administered in Two Intramuscular Doses to Healthy Adults aged 18 to 50 years. The targeted number of subjects is 270.The study 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 adultsTo 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 subpopulationsThis is a two center study; in which 270 healthy adults aged 18 to 50 years are randomly assigned to 1 of 9 groups; knowledge of rPA product received is double-masked, but schedule and receipt of AVA are unmasked. The duration of study participation is 12 months per volunteer following a screening period of no more than 30 days: administration over a 1- to 4-week period of two doses of IM rPA or 3 doses of SQ AVA with 12-14 follow-up visits. A subset of the approximately 45 volunteers who have agreed to participate in the special immunology subgroup (those with continued antibody responses at 1 year) will be offered extended participation beyond 1 year in which blood is drawn at 18 months, 2 years, 3 years, and 4 years for examination of long-term immune responses.