In this project, extensively characterized, live, attenuated vaccinstrains of Salmonella Typhimurium are made. These strains should evoke a good protection against a Salmonella infection in pigs and be attenuated in humans, animals and the environment. In addition, the pigs vaccinated with these strains, should be serologically distinguishable from pigs infected with field strains of Salmonella in the current national Salmonella pig control programme.