Toll-like receptor 2 (TLR2) deficiency enhances murine susceptibility to infection by Francisella tularensis as indicated by accelerated mortality, higher bacterial burden, and greater histopathology. Analysis of pulmonary cytokine levels revealed that TLR2 deficiency results in significantly lower levels of tumor necrosis factor alpha and interleukin-6 but increased amounts of gamma interferon and monocyte chemoattractant protein 1. This pattern of cytokine production may contribute to the exaggerated pathogenesis seen in TLR2-/- mice. Collectively, these findings suggest that TLR2 plays an important role in tempering the host response to pneumonic tularemia.