Specific-pathogen-free C57B 1 mice were vaccinated with one or two doses of 20 µg of heat-killed Salmonella enteritidis suspended in saline or in Freund's complete adjuvant. The saline-suspended vaccine did not protect against a subsequent oral challenge by a highly virulent strain of S. enteritidis (5694) but did increase resistance to a sublethal challenge with a partially attenuated strain (Se 795). Two doses of 20 μg of dead cells suspended in Freund's complete adjuvant sensitized the host so that an accelerated immune response could be demonstrated in mice infected orally with S. enteritidis 5694. This response was dose dependent. The highest dose of 500 μg of dead cells in adjuvant induced an immune response equivalent to that seen in actively infected mice. The significance of these findings in relation to immunity to typhoid was evaluated.