A S. typhimurium challenge model for swine was developed which takes into consideration both clinical changes and the colonization of various organs. Young swine were infected, using bait, with various doses of S. typhimurium DT 104 resistant to nalidixic acid. After infection, the presence of the challenge strain in the ileum, caecum and ileocaecallymph nodes was detennined quantitatively. The level of antibodies in the serum to S. typhimurium was established pre-challenge and 6 days after challenge using ELISA.