The basis of the different susceptibility to bacterial cell wall-induced arthritis between Lewis and Fischer rats is unclear. Likewise, it is not known why cell walls of some species of Lactobacillus are arthritogenic and those of others are not. With these two questions in mind, we investigated the role of anti-inflammatory (interleukin (IL)-10, IL-4) and proinflammatory (tumour necrosis factor (TNF)-alpha, IL-1 beta) cytokines in Lewis and Fischer rats injected intraperitoneally with cell walls from arthritogenic or nonarthritogenic species of Lactobacillus. Cytokine levels in the serum and in vitro production by peritoneal macrophages and splenocytes were studied. The results obtained indicate that the differences in the production of IL-10, IL-4, TNF-alpha or IL-1 beta do not explain the difference in the arthritis susceptibility between Lewis and Fischer rats. Likewise, the arthritogenicity of different Lactobacillus cell walls appears not to be dependent on their capacity to stimulate cytokine production.