The Mas-related gene family (Mrg), also known as SNSR (sensory neuron-specific G protein-coupled receptors), are expressed mainly in the dorsal root ganglia and appear to be involved in nociception and other sensory processes. MrgX1/SNSR4 is activated by the neuropeptide BAM22, and it mediates neuronal synaptic transmission and ion channel activity (Lembo et al., 2002; Burstein et al., 2006, Chen and Ikeda, 2004). Millipore’s cloned human MrgX1-expressing cell line is made in the Chem-1 host, which supports high levels of recombinant MrgX1 expression on the cell surface and contains high levels of the promiscuous G protein to couple the receptor to the calcium signaling pathway. Thus, the cell line is an ideal tool for screening for agonists and antagonists at MrgX1.