Attenuated strains of Salmonella enterica serovar Typhimurium are used as carriers of heterologous antigens as candidate oral vaccines and, more recently, as carriers of DNA vaccines. In this study, recombinant Salmonella strains that were altered in their ability to colonise murine tissues in vivo when compared to parent strains were not, however, equally altered in their ability to invade murine cells in vitro. These results suggest that in vitro invasion studies may not be a representative model for colonisation of tissues in vivo, and that in vitro studies should ideally be used in conjunction with in vivo studies for the assessment of potential Salmonella vaccines.