1. Glycine and lysine with the α-amino nitrogen labelled with 15N were fed to marasmic and recovered infants. The excretion of total 15N and labelled urea in the urine was followed for 72 h.
2. Excretion of 15N was lower in marasmic than in recovered infants for both amino acids. This was mainly due to a smaller amount of [15N]urea excreted by the marasmic infants.
3. [15N]Lysine was retained to a greater extent than [15N]glycine in marasmus and after recovery. This difference was more marked in marasmus. 15N in urea excreted by marasmic subjects after feeding with [15N]lysine was less than 5% of the total isotope administered.
4. The results suggest that requirements of marasmic infants for individual amino acids may differ considerably from those of the healthy infant.