To elucidate the mechanism of age-related development in FGS/NgaKIST mice with spontaneous glomerulosclerotic lesion, we examined expression and localization of various cytokine mRNA in the kidney in the progression of diseases. This mouse model is the first to develop spontanously occuring glomerosclerotic lesion in the kidney. In this study, we detected the up-regulation of local cytokine genes such as IL-1$eta$, IL-2, IL-6, IL-10, TNF-$alpha$, TGF-$eta$, and IFN- $gamma$ in the kidneys. In RT-PCR and Southern blot analysis, we detected gradual expressions of cytokine mRNA of IL-1$eta$, IL-2, IL-6, IFN- $gamma$, and TNF $alpha$ mRNA during the course of disease. Other cytokines including IL -10 and TGF -$eta$ were found to be appeared the slightly expressed level at 3 to 12 weeks before onset of inflammatory lesion but they are highly expressed at the end-stage of the disease accompaning high proteinurea and wasting. In situ RT-PCR, each cytokine mRNA were specifically localized in a variety of cells including mesangial, endothelial, parietal epithelial, tubular epithelial, arterial muscle cell, and infiltrated inflammatory cells. In addition, TNF - $alpha$was detected moderately in the visceral and parietal epithelial cell, but weakly in endothelial and mesangial cells, whereas IL-1 $eta$ and IL -6 were strong in mesangial regions. IL-6 and TNF- $alpha$ was highly localized in the damaged proximal and collecting tubules. Especially, TGF -$eta$ mRNA was highly found in mesangial cells within glomerulus and interstitium during the end-stage of this disease.. These results indicate that pro inflammatory cytokines such as IL-1 $eta$, IL-2, IL-6, and TNF- $alpha$ were gradually expressed from the early stage of this disease to the end-stage, and that IL-10 and TGF-$eta$ may be important in the accumulation of extracellular matrix(ECM) within glomerulus and periglomerular fibrosis in the progression of this disease as well as tissue destruction in end-stage of this disease.