The liver injury in the concanavalin A (Con A)-induced mouse hepatitis model has been well studied. However, there has been little study on the effects of Con A on extrahepatic organs. The aim of the present work was to determine the effects of Con A on the spleen, kidney and lung. A histopathological study showed that Con A (15 mg/kg, i.v.) administration affects not only the liver, but also all these extrahepatic organs. Messenger RNA expression was studied by the using polymerase chain reaction. Treatment with Con A induced interleukin-2 mRNA in the spleen, but only slightly induced it in the kidney. The mRNAs of interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α) were induced in all these organs. At 24 hr after Con A treatment, the expression of IFN-γ mRNA, but not that of TNF-α mRNA, was inhibited by cyclosporine A (50 mg/kg, i.p.), suggesting that Con A induced these cytokine mRNAs through different mechanisms. In the kidney and lung, CD4⁺ and CD8⁺ T-cell infiltration was suggested by the Con A-induced CD4 and CD8 mRNAs. The present study showed the histopathological effects of Con A and Con A-induced cytokine mRNA expression on the spleen, kidney and lung.