Prokineticins, also known as endocrine gland vascular endothelial growth factors (EG-VEGF), are two ~10 kD secreted proteins originally described to mediate angiogenesis and gastrointestinal smooth muscle contraction, and (Li et al., 2001; LeCouter et al., 2003). Subsequently, prokineticins have been found to mediate central nervous system functions including circadian rhythms and olfactory bulb development (Cheng et al., 2002; Ng et al., 2005). Two Gq-coupled receptors, PK1 and PK2 (also known as GPR73a and GPR73b), mediate cellular responses to prokineticins (Lin et al., 2002). The cloned human PK1-expressing cell line is made in the Chem-1 host, which supports high levels of recombinant PK1 expression on the cell surface and contains high levels of the promiscuous G protein Gα15 to enhance coupling of the receptor to the calcium signaling pathway. Thus, the cell line is an ideal tool for screening for antagonists of interactions between PK1 and its ligands.