Acidic glycosaminoglycans (AGAG) of human kidneys prepared from subjects of different ages were purified and determined by an enzymic assay with chondroitinases. The resulting disaccharide units and the undigested AGAG after digesting with the enzymes were identified by paper chromatography, electrophoresis and thin-layer chromatography. The age-dependent changes were: heparan sulfates accounted for 43–74% of total AGAG and the proportion to total AGAG appeared to decrease with advancing age. Dermatan sulfate remained without change. The proportion of hyaluronic acid appeared to decrease at 19–21 years and increased again with aging. The ratio of the 4-type chondroitin sulfate to the 6-type decreased with advancing age.