A recombinant strain of attenuated Salmonella enterica serovar Typhi surface-expressing Yersinia pestis F1 antigen was generated by transforming strain BRD1116 (aroA aroC htrA) with plasmid pAH34L encoding the Y. pestis caf operon. BRD1116/pAH34L was stable in vitro and in vivo. An immunisation regimen of two intranasal doses of 1 x 10(8) cfu of BRD1116/pAH34L given intranasally to mice 7 days apart induced the strongest immune response compared to other regimens and protected 13 out of 20 mice from lethal challenge with Y. pestis. Intranasal immunisation of mice constitutes a model for oral immunisation with Salmonella vaccines in humans. Thus, the results demonstrate that attenuated strains of S. enterica serovar Typhi which express Y. pestis F1 antigen may be developed to provide an oral vaccine against plague suitable for use in humans.