ABSTRACT: Stability of N-acetylglutamine (NAQ) in aqueous solutions from pH 2.0 to 8.0 and at 100 °C and in a liquid nutritional product was compared to glutamine using an improved HPLC method that allowed quantitation of degradation products. NAQ was stable for 6 mo at pH > 4.0 at about 20 °C. N-acetylglutamic acid, the major degradation, was found in samples stored for ≥ 2 wk. At pH 4.0 and higher, it remained at < 1% through 6 mo. At pH 2.0 and 3.0, N-(2,6-dioxo-3-piperidinyl) acetamide was also detected. Pyroglutamic acid formed at pH ≤ 3.0. No degradation of NAQ was observed in a liquid nutritional product (pH = 6.5) after 3 mo.