Protein is a major structural component of all cells in the body. The nutritional importance of protein is because of their amino acids. 9 are called essential and 11 are called non-essential, based on whether we need to get them from diet. This classification is based on studies done using older techniques. Recent studies suggest that these so called non-essential amino acids play important roles in our body's health. For the first time, this proposal defines an experimental design to examine non- essential amino acid/nitrogen requirements and metabolism in humans using the Indicator Amino Acid Oxidation (IAAO) technique.