Studies of morphology of the secretory hypothalamo-neurohypophyseal system under conditions of inhibition of the function of the peripheral region of the sympathetic nervous system were carried out. Desympathyzation was achieved by administration to newly born animals of antibodies to the factor of growth of nerves. In addition to the survey histological methods, morphometry, autoradiography and spectrophotometric investigations were also used. The aim of the work was to establish with the help of the methods referred to above the functional state of the hypothalamo-neurohypophyseal secretory system (HNSS) under deep immunological desympathyzation of the organism. The data obtained confirm the existence of a functional connection between the peripheral region of the sympathetic nervous system and HNSS. A hypofunctional state of the sympathetic department caused a rise in the functional activity to HNSS--in supraoptic and paraventricular nuclei of the hypothalamus there were observed enlarged neurones and their nuclei; this was accompanied by an intensification of the biosynthesis processes and secretion of neurosecretory material, neurohypophysis containing lesser amounts of neurosecret than in the norm. The rise of the functional activity of HNSS was accompanied by a higher specific hormonal effect upon the periphery (the effect of the hormone on "target"), which was confirmed by manifestations of working hypertrophy of the medullar of kidneys. The reaction of HNSS was apparently mediated through a complex of pathological changes in the organism and was directed at the maintenance of the optimal tonus of vessels and at preservation of homoestasis as a whole.