Histochemistry, cario- and zytometry methods showed that the activators of gastric secretion (histamine and pentagastrine) exerted opposite effects upon functional state of hypothalamo-neurohypophyseal secretory system in the guinea-pigs. Histamine (4 mg/kg) activated the system and induced the development of gastric mucosa defects. Pentagastrine (5, 12, 15, 25, and 60 mcg/kg) decreased the activity of the system. No gastric mucosa or duodenum defects developed after pentagastrine administration.