BACKGROUND Glutamine is a conditionally essential amino acid for patients with severe catabolic illness, intestinal dysfunction, or immunodeficiency syndromes. Glutamine is a natural component in many enteral preparations, yet lacking methodology hampers its quantitative determination in dietary products. OBJECTIVE The present study was assigned to assess glutamine contents in selected enteral products by using a newly developed method enabling the assessment of protein/peptide bound glutamine. METHODS Fourteen commercially available enteral diets (10 protein based and 4 peptide based) were investigated. After removal of interfering fat and carbohydrates, the nitrogen content of the purified preparations was determined by chemiluminescence and protein/peptide bound glutamine was assessed using a three-step procedure; by using a novel prehydrolysis derivatization technique with bis(1,1-trifluoroacetoxy)iodobenzene, glutamine is converted to acid stable diaminobutyric acid. The derivatives are hydrolyzed with a new microwave technology, and subsequently the amino acid composition is determined by reversed phase-high-performance liquid chromatography after dansyl-chloride derivatization. RESULTS The content in the protein-based preparations varied between 5.2 and 8.1 g/16 g nitrogen. In the peptide-based products, considerably lower glutamine contents were measured (1.3 to 5.6 g/16 g nitrogen). CONCLUSIONS In the present study, we report for the first time glutamine contents in ready to use enteral products. The daily amount might be satisfactory for healthy individuals but probably not sufficient for the adequate support of the stressed patient. Reliable assessment of glutamine in enteral formulae is a prerequisite t perform clinical studies investigating glutamine requirements in the catabolic state.