Analyses by anion exchange chromatography indicate that heparan sulfate proteoglycans isolated from the livers of experimentally diabetic rats have a reduced net negative charge as compared with heparan sulfate proteoglycans from control rats. In contrast, the size of the normal and diabetic proteoglycans are indistinguishable as are the size of individual polysaccharide chains when compared by gel chromatography. The reduced net negative charge of heparin sulfate from diabetic rats is shown to be caused by a reduced number of sulfate groups present in the diabetic heparan sulfate. Results are presented suggesting that one of the biosynthetic enzymes; the N-deacelylase, which tentatively has been identified as a regulatory enzyme affecting the sulfate content of the polysaccharide chains, may be inhibited in the diabetic rat.