Résumé : The brain gut octacosapeptide VIP (vasoactive intestinal peptide) is found in discrete areas in the cerebral cortex, the hypothalamus and the posterior pituitary gland. Specific VIP binding sites are coupled to an adenylate cyclase system in synaptic membranes from guinea pig brain. Besides, the concentration of VIP in the hypothalamo-hypophysial portal vessels is much higher than in the systemic blood. The peptide has however no established function in the hypophysis. These data document the presence in the rat pituitary of functional VIP receptors existing in the form of a VIP-stimulated adenylate cyclase system and suggest that VIP might be a major peptidic activator of rat adenopituitary membrane adenylate cyclase.