The metabolism of ground substance in connective tissue of an 18-year-old boy with oculo-cerebro-renal syndrome was studied. He had characteristic clinical and laboratory findings described by Lowe et al. such as growth retardation, mental deficiency, glaucoma, cataracta, decreased muscle tone, metabolic acidosis, aminoaciduria and osteomalacia. The urinary excretion of acid glycosaminoglycans and of total hydroxyproline were 27 mg/day (as glucuronic acid) and 280 mg/day respectively on admission. Both values decreased to the upper limits of normal level transiently during treatment with alkali and vitamin D2. At that time, an improvement in bone abnormalities, a decrease of serum alkaline phosphatase, and an elevation of serum inorganic phosphate were observed. The therapy prevented him from progressive osteomalacia and cured him of it, but mucopolysacchariduria and hydroxyprolinuria did not disappear. Analytical electrophoresis on cellulose acetate sheets showed that urinary acid glycosaminoglycans were composed of undersulfated chondroitin 4-/6-sulfate and heparan sulfate with a ratio of 6:4, on admission. After oral administration of alkali, the excretion of heparan sulfate decreased and undersulfated chondroitin 4-/6-sulfate was determined as a main component of urinary acid glycosaminoglycans. The clinical and laboratory data in this case suggested that the increased excretion of acid glycosaminoglycans and total hydroxyproline was caused by abnormal metabolism in connective tissues, especially by the bone abnormalities, in this syndrome.