OPPORTUNITIES to survey the newborn human infant for the occurrence of a wide variety of aminoacidopathies and to determine "normal" variation in plasma amino acid composition at this age have been rather limited. Most mass screening programs have focused on a single amino acid. The adaptation of simple modified partition chromatographic techniques1,2 to the analysis of amino acids in whole blood or plasma provided the opportunity to perform mass screening for many aminoacidopathies and to evaluate the worth of this endeavor. It was a subject of great interest to Dr. Efron,3 and one which she pioneered with Dr. MacCready and other colleagues until she could work no longer.
In this communication we report on a survey of 36,172 infants, in whom a measured volume of plasma was examined by partition chromatography. Our report follows that completed by Dr. Levy4 after Dr. Efron died, in which her survey