Abstract 1. 1. In extension of a previous report, posttraumatic nitrogen retention has been demonstrated with increasing doses of l-lysine monohydrochloride. The degree of retention was not found to be proportional to the dose of amino acid administered, and the absolute amount of retained amino nitrogen was small. The effect could be repeatedly demonstrated in the same dog following a suitable postoperative recovery period. 2. 2. Similar retention of amino nitrogen in plasma after injury has been found with dl-alanine, but not with a casein hydrolysate preparation. Determinations of alanine nitrogen per se suggest that the amino nitrogen retention observed is perhaps accountable on the basis of defective utilization of the individual amino acid administered. 3. 3. Starvation for the period of 120 hours had no significant effect on the plasma amino nitrogen concentration or on amino nitrogen loading responses. 4. 4. As previously observed, operative trauma was without effect on the post-absorptive plasma amino nitrogen concentration.