IN THE ever widening field of congenital metabolic defects, those characterized by mental retardation have attracted special interest.1 In some of these conditions the defect has been defined (galactosemia, phenylketonuria, maple syrup disease), resulting in more enlightened management. In others, effective therapy awaits more thorough understanding of the syndrome. The oculo-cerebro-renal (O-C-R) syndrome first described by Lowe in 19522 falls into the latter group. It is a congenital, inherited condition manifested by defects of the nervous system (mental retardation, hypotonia), eyes (cataracts, glaucoma), and kidneys. Biochemical abnormalities include metabolic acidosis, proteinuria, hyperaminoaciduria, and organic aciduria. Twenty-three cases have been reported to date.2-14 The purpose of this paper is to add eight additional cases to the literature and to present clinical, laboratory, and genetic studies of these patients and their families. Summary of Clinical Manifestations General Appearance.—Most of the patients in our series and those reported in the