The hallmark of end-stage renal disease is progressive sclerosis. The composition of the sclerotic material and its cellular source are under study and only partly elucidated. Sclerosis, in part, is composed of extracellular matrix components normal to the area, the sole exception thus far recognised is crescentic glomerulonephritis associated with Bowman's basement membrane disruption in which the sclerotic tissue contains interstitial connective tissue. The source of the extracellular matrix is the local glomerular cells. The complete composition of the extracellular matrix synthesised by individual glomerular cells is under current study, but it appears that all glomerular cells are capable of synthesising many of the various basement membrane components. The respective role of each cell type in sclerosing diseases and the initiating and propagating factors await further investigation.