The mouse model is widely used to study the mechanisms of the pathogenesis of, and immunity to, systemic salmonellosis. During infection, Salmonella grows in phagocytic cells that reside in well-defined pathological lesions, are activated by cytokines and control the growth of intracellular bacteria using oxygen and nitrogen derivatives. Salmonella growth in the tissues results in the spatial segregation of bacterial populations and in their continuous distribution to new phagocytes. High bacterial numbers within infected phagocytes are uncommon in vivo. (C) 2004 Elsevier SAS. All rights reserved.