PRP, also known as GPR10 or hGR3, is a Gq-coupled receptor for prolactin-releasing peptide that is expressed in the pituitary (Hinuma et al., 1998). Genetic studies in rodents indicate that lack of GPR10 leads to hyperphagia, obesity and dyslipidemia (Gu et al., 2004; Watanabe et al., 2005). In humans, genetic variations in GPR10 are associated with lowered blood pressure (Bhattacharyya et al., 2003). GPR10/PRP membrane preparations are crude membrane preparations made from our proprietary stable recombinant cell lines to ensure high-level of GPCR surface expression; thus, they are ideal HTS tools for screening of antagonists of GPR10/PRP interactions with prolactin-releasing peptide. The membrane preparations exhibit a Kd of 0.59-0.66 nM for [125I]-PRP-20. With 5 mg/well PRP Membrane Prep and 0.25 nM [125I]-PRP-20, a greater than 30-fold signal-to-background ratio was obtained.