In dogs with initially high level of gastric secretory activity (stimulated by carbachol), both preliminary and post-stressor infusion of glycilproline (Gly-Pro) (i) increased the gastric juice volume, the acidity, and the rate of hydrogen ion production inhibited by stress and (ii) potentiated the stress-induced decrease in the proteolytic activity. In the animals with initially low level of gastric secretion, the preliminary introduction of Gly-Pro led to an increase in the gastric juice volume, while the post-stress treatment reduced the juice volume, the acidity, the rate of production of active hydrogen ions (increased by immobilization). In both groups of animals, an increase in the content of fucose was observed in experiments with preliminary introduction of Gly-Pro.