L-glutamine is the most prevalent amino acid in the bloodstream and because human cells readily synthesize it, is usually considered a non-essential amino acid. It is found in high concentration in skeletal muscle, lung, liver, brain, and stomach tissue. Skeletal muscle contains the greatest intracellular concentration of glutamine, comprising up to 60 percent of total body glutamine stores, and is considered the primary storage depot and exporter of glutamine to other tissues. Under certain pathological circumstances the body’s tissues need more glutamine than the amount supplied by diet and biosynthesis. During catabolic stress intracellular glutamine levels can drop more than 50 percent, and it is under these circumstances that supplemental glutamine becomes necessary.1 In times of metabolic stress, glutamine is released into circulation, where it is transported to the tissue in need. Intracellular skeletal muscle glutamine concentration is affected by various insults, including injury, sepsis, prolonged stress, starvation, and the use of glucocorticoids. Therefore, glutamine has been re-classified as a conditionally essential amino acid. Research demonstrates glutamine supplementation may be beneficial when added to total parenteral nutrition (TPN) for surgery, trauma, and cancer patients. In addition, evidence suggests it may provide benefit for certain gastrointestinal conditions, wound healing, critically ill neonates, HIV/AIDS patients, immune enhancement in endurance athletes, and prevention of complications associated with chemotherapy, radiation, and bone marrow transplant.