A single dose 0.2 U/kg b.w. of insulin was administrated after an hour of infusion of pentagastrin 2 micrograms/kg b.w. for 6 healthy volunteers aged about 27 (22-30); the investigation was carried out for 1.5 h. The control group consisted of 6 health volunteers aged about 27 (21-36) which were administrated infusion of pentagastrin. While applicating stimuli the gastric juice was aspirated for analysis. In 15-minutes fraction of gastric juice the volume, concentration and output of hydrochloric acid, pepsin, protein and carbohydrates components of gastric mucus: hexoses, hexosamine, fucose and sialic acid were measured. It was stated that insulin decreases gastric secretion stimulated by pentagastrin in two first 15-minutes fractions after administration of insulin dependently on decrease of gastric juice volume. Insulin-hypoglycemia is a stimulus decreasing gastric mucus secretion, stimulated by pentagastrin. On this ground the conclusion can be arrived, that pentagastrin evokes the mechanism decreasing gastric mucus secretion, probably adrenergic. Insulin does not change hydrochloric acid secretion, but it appears to be en extremely strong stimulus for pepsin secretion which proves hypothesis, that secretion of this enzyme is regulated mainly by vagus.