Based on the human genome sequencing, 60% of the 800 GPCRs that have been identified belong to the so-called olfactory or sensory receptors. The remaining 40% are classified in five main families under the GRAFS system. In line with their pivotal role in a number of physiological processes, GPCRs have been found dysregulated in several human pathologies including cardiovascular and gastrointestinal diseases, nervous and immune disorders and cancers. As a matter of fact, nearly half of the drugs marketed by pharmaceutical industries targets GPCRs. In this context, highly specific anti-GPCR antibodies may be particularly helpful to better define anatomical localization as well as biochemical and biological properties of the receptors targeted for therapy. Antibodies may be used to reveal GPCR expression on living cells or on membrane extracts as well as in situ on fixed tissue sections. Specific antibodies may be helpful to purify receptors, characterize receptor dimers, identify receptor-associated protein partners, stabilize GPCR for crystallography, study ligand-binding kinetics and conformation states. In the absence of specific ligands, anti-GPCR antibodies are a valuable alternative for studying orphan receptors. Moreover, development of antibodies against GPCRs such as adhesion receptors, for which conventional small molecule drug discovery methods are often unsuccessful, offers a promising alternative for pharmaceutical industries. Approximately 80 GPCRs, Axitinib notably those involved in cancer, inflammatory or metabolic disorders have been recently identified as suitable targets for antibody-based therapy. Anti-GPCR antibodies, that do not cross the blood-brain barrier because of their high molecular weight, could also be instrumental in only targeting GPCRs expressed in periphery. Thus, agonistic antibodies with no central nervous system-mediated side effects might be used to relieve from inflammatory pain by stimulating opioid receptors expressed on sensory neurons. Specific antibodies against a variety of antigens including GPCRs can be developed using phage display technology, but the common method to produce antibody probes consists in immunizing animals against target proteins. As a matter of fact, most of the available anti-GPCR antibodies are polyclonal serum IgG generated by immunizing animals with synthetic peptides corresponding to amino-acid sequences located within the amino –terminal or carboxy -terminal domains or within extra or intra-cellular loops of the receptors. However, as recently reported for a number of GPCRs including opioid receptors, commercial available polyclonal antibodies often display non-specific reactivities and/or cross-reactivities with other plasma membrane proteins thus making it difficult to clearly distinguish a specific antibody-receptor binding. In most of the cases, the staining patterns of anti-GPCR peptide antibodies are similar in wild-type and GPCR-deficient mice as assessed by immunohistochemistry or western-blotting. A recent study, comparing the specificity of a number of commercial anti-opioid receptor antibodies, has shown that all the antibodies revealed numerous non-specific bands including a band at the expected molecular weight in both wild-type CHO cells and GPCR-expressing CHO cells as assessed by western-blotting. Given the lack of specificity of anti-GPCR peptide antibodies with receptors in native conformation.