Glycosaminoglycans and glycoproteins in the urine of 100 healthy, active, human subjects were examined by cellulose acetate electrophoresis and salt gradient, ion-exchange, column chromatography. The cetylpyridinium chloride (CPC) turbidity and uronic acid:creatinine ratio was also studied. Fractions were identified by electrophoretic mobility, staining reactions, susceptibility to enzyme digestion, identification of amino- and neutral sugars, hexosamine, uronic acid, and sulphate assays, and optical rotation. The CPC turbidity is relatively high in childhood, falling to lower levels in adults, but rising again to relatively high levels in old age. The uronic acid: creatinine ratio is high in children, falling to a low level in adult life, and rising only slightly in old age. Three major electrophoretic fractions, corresponding with glycoprotein, heparan sulphates, and chondroitin sulphates, were identified in every urine sample. Hyaluronic acid was identified in some samples. A small amount of keratan sulphate was present in the ;heparan sulphate' fraction. Chondroitin sulphate excretion is high in children. Adults excrete relatively less chondroitin sulphate and more heparan sulphate. In old age, the proportion of glycoprotein increases. The excretion pattern in the first few days of life resembles that of the adult. It is stressed that extreme caution must be exercised in interpreting the urinary glycosaminoglycan pattern of a child.