Parenchymal deposits with the histochemical characteristics of acid glycosaminoglycans were discovered in the brains of 12 chimpanzees ranging from 6 months gestational age to 17 months post partum. Similar deposits were not seen in the brains of one fetus of approximately 3 1/2 month gestational age or in the brains of three animals that were 10 or more years of age. The deposits were found primarily in thecapsula interna, lentiform nucleus, andcapsula externa. Only a few deposits were located in the thalamus. In most instances, the mucopolysaccharid deposits were surrounded by accumulations of glial cells indicating a weak to moderate glial reaction.