The aim of this study was to elucidate the distribution of extracellular matrix(ECM)proteins in glomeruli and renal interstitium in various forms of glomerulonephritis(GN).Interstitial fibrosis is the best sole prognostic factor for all histological forms of GN, except for rapidoprogressive GN.There is a statistically significant positive correlation between relative renal cortex interstitial volume and creatinin serum level. We examined normal renal tissue and 55 renal biopsies from patients with various forms of GN by immunohistochemistry(APPAP-method)using monoclonal antibodies against tenascin(TN), fibronectin(FN)and collagen I, III and IV(COI, COIII, COIV). In normal renal tissue glomerular mesangium is TN, FN and weakly COI positive.Glomerular and tubular basement membranes stained with COIV antibody.There was a weak COI expression in interstitium.Intensive TN staining was found in medullar interstitium only.Epithelial cells of proximal tubules and medullary collecting ducts showed COI and COIII staining, while TN was detected only in proximal tubules.The wall of larger blood vessels was TN, FN and COI positive. Irrespectively of histological form of GN, foci of glomerular sclerotis were TN, FN, COI, COIII and COIV positive.In focal segmental glomerulosclerosis(5 cases)mesangium, apart from sclerotic foci, was FN negative.There was sometimes de novo COIII and COIV staining of mesangium in GN with mesangial proliferation.Fibrous crescents showed TN, FN, COI, COIII and COIV staining.Thickened Bowmans capsule expressed COI, COIV and TN. At sites of interstitial inflammation there was de novo TN expression, while at sites of interstitial fibrosis FN and COIV were invariably present.TN was found in fibrosis in 20 of 33 cases with interstitial fibrosis, mainly in biopsies with concomitant interstitial inflammation.COIII staining was found at sites of fibrosis only in 5 biopsies.COI was expressed more intensively in the interstitium when inflammation and fibrosis were present. Our results show that there is a marked change of mesangial and interstitial ECM in various forms of GN.Some constituents, like TN, seem to be essential for proliferation, while others represent invariable constituents of sclerosis/scar ECM.