Bombesin, a bioactive peptide first identified in amphibian skin, is related to two mammalian peptides, gastrin-releasing peptide (GRP) and neuromedin B. A family of 3 GPCRs, including NMB-R (BB1), GRP-R (BB2) and BRS-3 (BB3), mediate the biological effects of the peptides. The receptors differ in their affinities for the peptides; BB2 binds to GRP with 50-300-fold greater affinity than to NMB, whereas BB1 binds to NMB with 10-800-fold greater affinity than to GRP (Tokita et al., 2004). Binding of ligand to BB2 activates Gq to increase intracellular calcium concentrations. GRP stimulates release of gastrin from endocrine cells and stimulates smooth muscle activity in the gastrointestinal tract. In addition, binding of GRP to BB2 stimulates proliferation of a variety of cell types, and has been implicated in the progression of small cell lung cancer and other malignancies. The CNS is also a major site of GRP expression, and GRP and BB2 are involved in the circadian clock, conditioned fear, and food intake (Ohki-Hamazaki et al., 2005). Chemicon's cloned human BB2-expressing cell line is made in the Chem-1 host, which supports high levels of recombinant BB2 expression on the cell surface and contains high levels of the promiscuous G protein G°15 to enhance coupling of the receptor to the calcium signaling pathway. Thus, the cell line is an ideal tool for screening for antagonists of interactions between BB2 and its ligands.