Research was reviewed on the current status of phenylketonuria, an hereditary amino acid metabolic disorder that can cause severe mental retardation, physical complications, and emotional difficulties if not detected and treated early in childhood. A majority of the research cited was published in the 1960's. Topics covered were: discovery of phenylketonuria; etiology; incidence; clinical syndrome; possible resulting mental retardation; frequent common physical characteristics; possible resulting neurological disorders; detection techniques through urine, blood, fluorometric, and chromotographic screening tests; considerations on dietary treatment; usual positive effects of treatment; treatment problems concerning acceptance of treatment by parents, acceptance by child himself, and regular medical surveillance; and anticipatory and corrective measures for prevention of phenylketonuria. A bibliography of about 70 documents and a listing of states having mandatory screening laws were included. (CB)