Bombesin is a 14-amino acid peptide originally isolated from the skin of a frog. It has two known homologs in mammals called neuromedin B and gastrin releasing peptide. It stimulates gastrin release from G cells. It activates three different G-protein-coupled receptors known as BBR1 2 & 3. It also activates these receptors in the brain. Together with cholecystokinin, it is the second major source of negative feedback signals that stop eating behaviour.

Bombesin is also a tumor marker for small cell carcinoma of lung, gastric cancer, and neuroblastoma. Bombesin is a polypeptide that is found in the brain and gastrointestinal tract and has been shown experimentally to cause the secretion of various substances (as gastrin and cholecystokinin) and to inhibit intestinal motility