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. 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). BB2 membrane preparations are crude membrane preparations made from our proprietary stable recombinant cell lines to ensure high-level of GPCR surface expression; thus, they are ideal HTS tools for screening of antagonists of BB2 interactions and its ligands. The membrane preparations exhibit a Kd of 0.114 nM for [125I]-Tyr4-Bombesin. With 0.3 nM [125I]-Tyr4-Bombesin, 5 mg/well or 10 mg/well BB2 Membrane Prep typically yield greater than 20-fold signal-to-background ratio.