Relaxin-3 is highly expressed in nucleus incertus neurons and is implicated in the control of stress responses, arousal/attention, anxiety/mood, feeding/reward and cognition (see (1)). Neurotensin is also widely expressed in the central nervous system where it acts as a modulator of the classical transmitters, dopamine and glutamate, and is implicated in the pathogenesis of Parkinson’s disease and schizophrenia. Neurotensin and relaxin-3 act via their respective, cognate G-protein-coupled receptors (GPCRs), neurotensin receptor 1 (NTS1) and relaxin family peptide receptor 3 (RXFP3). A lack of knowledge about the molecular mechanisms underlying ligand binding and activation of these receptors hinders the discovery and design of small molecules targeting NTS1 and RXFP3. The instability of GPCRs upon purification is the major hindrance to structural and biochemical studies of these proteins. We use protein engineering to produce receptor variants that are highly stable upon purification. A directed-evolution technique, ‘CHESS’ (Cellular High-throughput Encapsulation, Solubilisation and Screening), allows the direct selection of detergent-stable GPCR mutants from large gene libraries containing greater than 108 individual receptor variants. CHESS has been applied to several Class-A GPCRs, including NTS1 (2) and more recently RXFP3, resulting in several X-ray crystal structures (3). These stabilised GPCRs are valuable tools for biochemical and structural studies that were previously difficult to perform using unmodified receptors. One such method is nuclear magnetic resonance spectroscopy (NMR), which we are using to discover new binding sites in NTS1 and identify new molecules to target this receptor. It is hoped that such studies will further our knowledge about this critical class of signalling proteins and lead to identification of new lead compounds for drug development.