1. A study was made of the metabolism of ɛ-(γ-L-glutamyl)-L[4, 5-3H]lysine (GL) in the rat.
2. The compound was largely absorbed from the intestine and metabolized. Labelled lysine was incorporated into blood proteins.
3. In an in vitro experiment with everted sacs of rat small intestine, GL passed through the intestinal wall unchanged.
4. The results of comparative tests using homogenates of different body tissues indicated that the kidneys were particularly active in hydrolysing GL. Their activity was nine times greater than that of the liver and eighteen times greater than that of the small intestine.