Bombesin is a 14 amino acid peptide isolated from frog skin. The mammalian counterparts are neuromedin B (NMB) and gastrin-releasing peptide (GRP). Three bombesin receptor subtypes (BB1, BB2 and BB3) have been classified in humans according to the rank order of potency to the endogenous ligands: NMB, GPR and bombesin. BB1 binds to NMB with 10-800-fold higher affinity than GRP and is also named NMB receptor, whereas BB2 binds to GRP with 50-300-fold higher affinity than NMB and therefore named GRP receptor. BB2 receptors are widely distributed in the CNS as well as in the gastrointestinal tract and reproductive organs. In CNS, Bombesin-like peptides induce satiety and play a role in thermoregulation and induce histamine-independent pruritus. These peptides also act via the BB2 receptor to regulate sleep disorders, depression and involved in the regulation of emotionally motivated learning, memory and food intake. In the gastrointestinal tract, GRPR receptors are involved in smooth muscle contractility, pancreatic secretion and the release of many other gastrointestinal peptides.