1. A micromethod for the determination of amino acids by ion exchange chromatography was applied to the quantitative determination of the free amino acids in 0.1 ml of plasma of the newborn infant. The precision of the method was in general within the range ± 5%. An interpretive analysis of a typical chromatogram is given. 2. Plasma was best stored at -68°C pending analysis; errors likely to arise on storage at -20°C and higher temperatures are pointed out. Some errors likely to arise in the preparation and storage of plasma protein free filtrates are also indicated. 3. Comparison of the free amino acids in the femoral vein plasma of 25 newborn infants was made with the literature values of the free amino acids in the plasma of adults. The differences noted were not great, but were apparently characteristic. On comparing heel puncture plasma, some amino acids were higher than in femoral vein plasma, but it was concluded that heel puncture plasma would be satisfactory for routine clinical purposes. Some possible sources of error which might explain the elevated amino acids in the heel puncture plasma were noted. 4. On comparison of newborn with 3-day-old infants, some changes in amino acid levels were noted. The changes were not great, but seemed to be characteristic and consistent. 5. A number of small peaks which have not been noted previously in plasma have been indicated on the chromatogram. They were not identified, but were mentioned to draw attention to the possibilities of hitherto unrecognized ninhydrin-positive components of plasma.