Human mas-related genes such as MRGPRD are members of the seven transmembrane spanning G protein coupled receptor super family implicated in the sensation and transmission of noxious stimuli such as pain and itch, hence intervening with these may prove useful in the management of unmet patient need. To date there have been few reports of the generation of inhibitors of these receptors. To provide new tools to aid the effort in discovering new agonists and antagonists here we describe the use of a label-free assay to study the pharmacology of MRGPRD and compare it to other more traditional methods such as intracellular calcium release.