The existence of a new hypothalamic regulatory pathway of pancreatic insulin secretion is described and experimentally proved. This paraventriculovagal pathway connects though neural conductors (in particular, the vagus nerves) hypothalamic paraventricular neurons with pancreatic islets allowing for the parahypophyseal bypass regulation of insulin secretion. This pathway stimulating insulin secretion interacts with another (transhypophyseal) hypothalamic regulatory pathway that inhibits insulin secretion and involves hormones of the pituitary-adrenal gland system (ACTH-glucocorticoids). Thus, regulation of insulin secretion is effected through the interaction between the transhypophyseal (inhibitory) and parahypophyseal (stimulatory) regulatory pathways. Both these pathways are triggered by peptides of the immune system (interleukin-1) via a feedback mechanism. Hence, the mechanisms of hypothalamic regulation of the carbohydrate homeostasis provide an example of the interaction between three regulating systems — the nervous, endocrine, and immune systems. The interaction between these systems attracts now considerable attention. Accumulated evidence provides the grounds to consider neuroimmunoendocrinology as a new field of scientific knowledge. The described regulatory system can be used as a convenient biological model for neuroimmunoendocrinological studies.