We compared the distribution of the α1 and α2 chains of collagen IV and of collagens V and VI in glomeruli of males with Alport syndrome to their distribution in normal glomeruli and glomeruli from patients with non-Alport renal diseases. α1(IV), α2(IV), collagen V and collagen VI are normally restricted to the mesangium and the subendothelial aspect of the glomerular basement membrane (GBM). In contrast, these proteins were present throughout the entire width of the GBM in Alport glomeruli. These alterations were apparent in "early" Alport glomeruli, that is, those exhibiting minimal abnormalities by light microscopy, and they were further accentuated in sclerosing Alport glomeruli. Obsolescent Alport glomeruli, in which the capillary tuft had collapsed and few remaining cell nuclei were present, exhibited nearly complete loss of α1(IV) and α2(IV), like obsolescent glomeruli in non-Alport diseased kidneys. However, the matrix of obsolescent Alport glomeruli stained intensely for collagen V and collagen VI, while these collagen types were not prominent in obsolescent glomeruli of non-Alport diseased kidneys. These observations suggest that the process of glomerulosclerosis in Alport kidneys has attributes unique to this disease. It would also appear that mutations affecting the Alport gene product have secondary effects on the distribution of other GBM constituents.