Prostanoids are a series of arachidonic acid metabolites produced by the action of cyclooxygenase and subsequently by isomerases and synthases. Cells rapidly secrete prostanoids after synthesis, whereupon the prostanoids bind to a family of 8 GPCRs to exert their biological effects (Narumiya and FitzGerald, 2001). The prostaglandin PGD2 is produced by mast cells upon activation by allergens, and is present at high levels in allergic diseases. PGD2 binds to two receptors, DP and CRTH2. DP activates Gs to increase cAMP levels, and lack of DP results in reduced allergic response in animal models of bronchial asthma (Matsuoka et al., 2000). Cloned DP receptor-expressing ChemiBrite cells were made by stable transfection of HEK293 cells with ChemiBrite clytin, the DP Receptor and a promiscuous G protein to couple the receptor to the calcium signaling pathway. These stability-tested cells are ready for luminescent analysis of agonists, antagonists and modulators at the DP receptor.