The peptide neurotransmitter vasoactive intestinal polypeptide (VIP) has several important functions in vertebrates, particularly, influencing the neuroendocrine and autonomic nervous systems both in developing and in adult animals. To document potential brain areas that might play significant functional roles, the distribution of VIP mRNA was examined throughout the entire chick brain by using in situ hybridization histochemistry (ISHH). In addition, a VIP binding-site study was completed that focused on the lateral septal organ (LSO), a circumventricular organ of potential significance in avian species. The areas where VIP message was found included the olfactory bulbs, posterior hippocampus, parahippocampal area, hyperstriatum, archistriatum/nucleus (n.) taenia (amygdala), medial part of the LSO, organum vasculosum of the lamina terminalis, medial preoptic region, bed n. of the pallial commissure, anterior hypothalamic (hypo.) n., lateral hypo. area (most extensive and dense message), periventricular hypo. n., lateral to the paraventricular n., ventromedial hypo. n., stratum cellulare externum, inferior hypo. n., infundibular hypo. n., median eminence, three layers within the stratum griseum et fibrosum superficiale, area ventralis of Tsai, n. tegmenti pedunculopontinus pars compacta (substantia nigra), intercollicular n., central gray, locus ceruleus, parabrachial n., ventrolateral medulla, reticular pontine area, in and about the n. vestibularis descendens. When compared with immunocytochemistry that detected the presence of the peptide product VIP, more areas of the brain were found to contain perikarya expressing VIP by using ISHH, particularly in the telencephalon and the mesencephalon. VIP binding sites were found in the lateral portion of the LSO where the blood-brain barrier is not fully developed. Hence, the LSO was found to contain neural elements that synthesize as well as bind VIP. VIP appears to be a useful peptide for defining major components of the visceral forebrain system in birds.