Given the notorious variability in the protective efficacy of the current tuberculosis (TB) vaccine, BCG, in diverse populations around the world, there is a clear need for an improved TB vaccine. Although a major scientific effort over the past several years has produced literally hundreds of potential TB vaccine candidates, very little research has gone into alternative delivery systems and new adjuvants which will be required for purified protein or peptide vaccines. More importantly, given the pulmonary route of exposure by which most TB patients acquire their primary infection, it is surprising that little data derived regarding aerosol vaccination can be found in the recent biomedical literature. There are many reasons, a priori, to expect that direct immunization of the lung would have intrinsic advantages over parenteral routes of vaccination. Delivery of immunogens and adjuvant to the alveolar spaces using a microparticle aerosols should elicit local immune responses, which are effective at controlling the early replication of virulent Mycobacterium tuberculosis (MTB). Expertise in microparticle formulation, pulmonary aerosol delivery, a guinea pig model of low-dose pulmonary MTB and guinea pig immunology will be employed to elucidate the mechanisms by which aerosol vaccination leads to protection against virulent challenge. It is proposed that: (1) Lung delivery of immunostimulatory adjuvants (Muramyl dipeptide and trehalose dimycolate) in microparticle formulations will upregulate proinflammatory and co-stimulatory functions in resident alveolar macrophages; (2) The combination of immunogenic mycobacterial proteins with the adjuvant in microparticles will induce a strong expression of local antigen-specific T and B lymphocyte responses in the lung; (3) Aerosol vaccination with the optimal combination of protein antigen (Ag 85 complex)/adjuvant/micro-particles will protect guinea pigs against low-dose pulmonary challenge with virulent MTB. The significance of this work lies in the novelty of pulmonary vaccination for the treatment of tuberculosis and the knowledge of the immune response gained from targeted antigen delivery to the lungs.