Live attenuated bacterial vaccines allow vaccination via the mucosal surfaces and specific targeting to professional antigen presenting cells located at the inductive sites of the immune system. A novel approach exploits attenuated intracellular bacteria as a delivery system for eukaryotic antigen expression vectors (so-called DNA vaccines). Candidate carrier bacteria include attenuated strains of Salmonella, Shigella and Listeria spp, which have been shown, in vitro, to deliver DNA vaccines to human cells. Bacterial DNA vaccine delivery has also demonstrated in vivo efficacy in several experimental animal models of infectious diseases and tumors. The next step should be the clinical assessment of the safety, immunogenicity and efficacy of DNA vaccine delivery by live bacterial vaccines.