Sodium chondroitin sulfate A and sodium hyaluronate were subjected to hydrazinolysis and the non-dialyzable and dialyza ble products of the hydrazinolyzates were examined.Only small amounts of hydrazinolyzed products of these acid mucopolysaccharides passed through cellophane membranes. By the hydrazinolysis, the decomposition of glucuronic acid was scarce whereas approximately 10 per cent of total hexosamines were degraded.Besides small amounts of some unknown degradation products, small amounts of 2,5-anhydrohexoses and pentoses (lyxose from the chondroitin sulfate A and arabinose from the hyaluronate) were found in the hydrazinolyzed products. These sugars were thought to be intermediates in the degradation reaction of N-acetylhexosamines by the hydrazinolysis.The :per cent N-deacetylation by the hydrazinolysis of N-acetylgalactosamine in sodium chondroitin sulfate A and of N-acetylglucosamine in sodium hyaluronate amounted to 28.2 per cent and 22.9 per cent, respectively. Approximately 36 per cent of the N deacetylated hexosamines in the non-dialyza ble products of the hydrazinolyzates could be determined as 2, 5-anhydrohexoses by the direct deamination with nitrous acid.Sulfates in the sodium chondroitin sulfate A remained in the non-dialyzable product of the hydrazinolyzate.