The induction of signal transducer and activators of transcription (STATs) in macrophages is necessary for cellular activation, and we investigated the activation of STAT3 in these cells following infection with Salmonella. Increased activation of STAT3 was observed at 6 and 24 h post-infection in the mesenteric lymph nodes and spleens when compared to control mice. CD11b+ cells isolated from the mesenteric lymph nodes of infected mice demonstrated increased STAT3 activation as early as 6 h following infection. Culturing bone marrow-derived macrophages with Salmonella resulted in translocation of STAT3 to the nucleus and STAT3 phosphorylation as early as 30 min post-exposure. Increased STAT3 activation was also observed in the lymphoid organs or in macrophages from mice deficient for IL-6 or IL-10 production following infection. Taken together, these studies clearly demonstrate an early increase in the activation of STAT3 in vivo and in vitro following infection with wild type Salmonella.