Salmonella infection of the intestinal tract results in damage to the gut epithelium. While it is generally believed that bacteria and/or bacterial products account for this pathology, the role of host factors has not been explored. Using a ligated intestinal loop model, we investigated whether tumor necrosis factor-alpha (TNF-alpha) could contribute to the tissue pathology associated with Salmonella infection. Intestinal segments infected with Salmonella typhimurium had high levels of fluid secretion as early as 6 h post-bacterial infection. At this time point, low levels of TNF activity were also present in the fluid obtained from infected segments. At 20 h post-infection, high levels of TNF activity were present in fluids obtained from infected intestinal segments and was characterized as TNF-alpha by neutralization experiments using rabbit antisera to TNF-alpha. TNF-alpha production was further verified by Northern blot analysis using RNA obtained from cells eluted from the infected intestinal segments. In contrast, no TNF activity was found in fluid obtained from intestinal segments challenged with cholera toxin, which induces fluid secretion with little to no inflammatory response. Double labeling by in situ hybridization and immunocytochemistry revealed that macrophages in the lamina propria were producing the TNF-alpha mRNA. To investigate what role TNF-alpha might play in Salmonella-induced inflammation, intestinal segments were injected with recombinant mouse TNF-alpha (rTNF-alpha) or mice were pretreated with antibody to TNF-alpha or a control antibody prior to Salmonella infection. The histological profile of intestinal segments injected with rTNF-alpha appeared identical to segments infected with S. typhimurium. Further, pathology was completely eliminated in infected mice pretreated with antibody to TNF-alpha. These results document the production of TNF-alpha in the intestinal tract following S. typhimurium infection and show that the early pathology induced by Salmonella infection of the gastrointestinal tract is mediated by immune mechanisms.