Phenylketonuria is a disease characterized by the inability to metabolize an essential amino acid, phenylalanine, which is present in all proteins in average concentration of 4%. Phenylalanine, phenylpyruvic acid, ortho-hydroxyphenylacetic acid, and other unusual metabolites are excreted in the urine. This biochemical abnormality ordinarily leads to severe mental defect. Excellent reviews1 have appeared recently.
Results have been reported2 indicating that treatment with diets low in phenylalanine has been successful in allowing normal physical and mental growth. It appears, therefore, increasingly important to detect phenylketonuria in early infancy. A routine diaper test3 has been in use in southern California for some time.
Collection of urine specimens from infants is always difficult. Urine containing phenylpyruvic acid that has been dried on filter paper gives a positive test with ferric chloride reagent even after several months. We have devised a simple method for collection of urine on filter paper which