The urine of untreated phenylketonurics in the first weeks of life contains gamma-glutamylphenylalanine (0.07--0.69 mmol/g creatinine, 12 samples) visible on the normal 2-dimensional electrophoreto-chromatogram. This compound is less prominent or absent when urine from older untreated phenylketonurics is examined and is not seen in normal urine.
