Interleukin-18 (IL-18) is a recently cloned cytokine, produced from activated macrophages, including Kupffer cells. IL-18 is originally called interferon-gamma inducing factor (IGIF), due to its action to induce IFN-gamma production from Th 1 cells and NK cells. However, recent studies suggested that, IL-18 also enhances expression of FasL and NK activity as well as GM-CSF production. These data revealed this novel cytokine is pleiotropic. Recently, cDNA encoding human IL-18 receptor (IL-18R) was cloned. And, we had cloned murine IL-18R cDNA by RT-PCR, using human IL-18R sequence. Northern blot analysis of cytoplasmic RNA from T cells stimulated with IL-12 clearly demonstrated that, T cells stimulated with IL-12 induced high level of IL-18R-mRNA, whereas non-stimulated T cells did not have. Interestingly, we had several reports, indicated the involvement of IL-18 on the progressions of pathogenicity in chronic inflammatory diseases, including endotoxin-shock, hepatitis and autoimmune-diabetes. We need further studies to reveal physiological roles of this novel cytokine in various inflammatory or autoimmune diseases.