The human glomerular basement membrane belongs to the collagen family of proteins. It contains about 7 percent carbohydrate, half of which occurs as glucosylgalactose disaccharide units linked to hydroxylysine. Glomeruli from diabetics contain increased amounts of basement membrane material. In addition, these membranes show a distict chemical alteration c haracterized by a significant decrease in lysine, accoumpanied by an equivalent increase in hydroxylysine and hydroxylysine-linked disaccharide units.