The author reviews the problems in the laboratory diagnosis of gastric diseases. Physical and chemical changes in the gastric juice during chronic gastritis, peptic ulcer, Addison-Biermer's disease are described, as are changes in the gastric acid and enzyme production in these conditions. In cases when gastric secretion cannot be examined with a thin tube, methods not involving the use of a tube are recommended, that give a preliminary picture of gastric secretion. Microscopic examination of the gastric juice obtained on an empty stomach detects congestion and impaired evacuatory function of the stomach.