In order to evaluate the immunogenicity and protective efficacy of anthrax vaccine candidates a suitable small animal model is required. The inbred A/J strain of mouse has been selected as a potential model, and its immune response to immunisation with recombinant protective antigen (rPA) vaccine characterised, by assessment of rPA specific antibody production, and protection against injected challenge, with the unencapsulated STI strain of Bacillus anthracis. Studies were conducted to determine the time required post immunisation to develop a protective immune response, to define the minimum protective dose of vaccine required and to assess the long-term immune response to immunisation. From the results of these studies it was possible to establish that the A/J mouse is a consistent and robust small animal model for rPA vaccine testing. A comparison of the immune response to rPA vaccine immunisation in the Turner Outbred (TO) mouse strain was also conducted. Both inbred and outbred mouse strains displayed a predominantly Th2 biased immune response and showed a comparable antibody response to rPA immunisation. An assessment of protection in the TO mouse against aerosol challenge with the fully virulent strain of B. anthracis, Ames, was also made.