Content of free glutamine and the activity of glutamine synthetase and glutamine transaminase were studied in practically healthy persons and in patients with chronic atrophic gastritis, ulcerous disease, polyposis and with gastric carcinoma. The enzymatic activity was estimated in the areas of ulcerous impairment, of polypous vegetation of malignant neoplasm as well as in mucous membrane out of the impaired zone and in whole blood of all the patients studied. The tissues for biochemical tests were obtained by the directed gastrobiopsy. Content of glutamine was decreased in blood of patients with gastric carcinoma and increased in mucous membrane adjacent to the malignant tissue. Occurrence of the glutamine transaminase activity in the tissue areas studied was due to the specific glutamine metabolism during pretumoral diseases and gastric carcinoma, whereas the unimpaired gastric mucosa did not have the distinct enzymatic activity.