Vasoactive intestinal peptide (VIPb) and pituitary adenylate cyclase-activating polypeptide (PACAP) are members of a superfamily of structurally related peptide hormones that includes glucagon, glucagon-like peptide, secretin, and growth hormone-releasing factor (GRF). At least three receptors for PACAP exist in mammals, two of which are also high-affinity receptors for VIP. This report, prepared by the IUPHAR Subcommittee on Nomenclature for Receptors for VIP and PACAP, proposes a scheme of nomenclature for these receptors (table 1). VIP, first isolated from porcine intestine as a 28 amino acid peptide capable of inducing vasodilation in the canine femoral artery (Said and Mutt, 1970, 1972), subsequently has been shown to have many other actions as a neuroendocrine hormone and putative neurotransmitter. The presence of VIP and specific VIP binding sites in defined pathways in the brain indicates that it may play an important role in central nervous system (CNS) function (Besson et al., 1986; Martin et al., 1987). VIP also may promote neuronal survival (Brenneman and Eiden, 1986) and regulate glycogen metabolism in the cerebral cortex (Sorg and Magistretti, 1992). VIP stimulates prolactin secretion from the pituitary (Reichlin, 1988) and catecholamine release from the adrenal medulla (Malhotra et al., 1988); in the immune system it inhibits mitogen-activated proliferation of T cells by inhibiting interleukin-2 production (Ottaway, 1987). Other actions of VIP include stimulation of electrolyte secretion, smooth muscle relaxation, and protection against oxidant injury (Gozes and Brenneman, 1989; Laburthe et al., 1993; Said, 1991, 1996). In common with the precursors of several other neuroendocrine peptides, the VIP precursor polypeptide (prepro-VIP) contains sequences encoding additional biologically active peptides, including peptide histidine isoleucine (PHI; Tatemoto and a Address for correspondence: Anthony J. Harmar, MRC Brain Metabolism Unit, University Department of Pharmacology, 1 George Square, Edinburgh EH8 9JZ, UK. E-mail: Tony. Harmar@ ed. ac. uk. b Abbreviations: cDNA, complementary deoxyribonucleic acid; CNS, central nervous system; GRF, growth hormone-releasing factor; mRNA, messenger ribonucleic acid; PACAP, pituitary adenylate cyclase-activating polypeptide; PHI, peptide histidine isoleucine PHM, peptide histidine methionine; PHV, peptide histidine valine; SCN, suprachiasmatic nucleus; VIP, vasoactive intestinal peptide.