Motilin is a 22 amino acid peptide that potently stimulates gastrointestinal contractility. The biological effects of motilin are mediated by a Gq-coupled seven transmembrane protein, currently termed motilin receptor (MR), that shares significant sequence similarity with the ghrelin receptor (Feighner et al., 1999). The motilin receptor is also activated by the antibiotic erythromycin; this interaction appears to mediate some of the gastrointestinal side effects of erythromycin. Although motilides (non-antibiotic derivatives of erythromycin) such as ABT-229 have been investigated for treatment of diabetic gastroporesis, the effectiveness has been limited by tachyphylaxis (decreased response to ligand) resulting from receptor downregulation (Thielemans et al., 2005). Agonists of the motilin receptor with reduced densensitization activity remain a potential treatment for disorders of gastric motility. The cloned human Motilin Receptor-expressing cell line is made in the Chem-1 host, which supports high levels of recombinant Motilin Receptor expression on the cell surface and contains high levels of the promiscuous G protein Gα15 to couple the receptor to the calcium signaling pathway. Thus, the cell line is an ideal tool for screening for antagonists of interactions between the Motilin Receptor and its ligands.