Interleukin 6 (IL-6) is a polypeptide mediator regulating immune response, acute phase reaction and hematopoiesis. Disregulating production of IL-6 was suggested to be involved in a variety of chronic inflammatory diseases. IL-6 is an autocrine growth factor for cultured mesangial cells. IL-6 was localized in the mesangial area of the kidney tissue and intraglomerular expression of mRNA, encoding for IL-6 gene, was observed in patients with mesangial proliferative glomerulonephritis (mes PGN). Furthermore, mesangial proliferation was observed in IL-6 transgenic mice. These results suggest that IL-6 is closely associated with the pathogenesis of mesPGN.