GPR40 is a seven transmembrane G Protein-coupled receptor with signalling mediated by medium- and long-chain fatty acids. Found predominantly in the .beta.-cells of pancreatic islets, it has been implicated in the regulation of insulin secretion. Overexpression of GPR40 in mouse .beta. cells leads to glucose intolerance suggesting a link between GPR40 expression and diabetes. The receptor has also been identified as a possible mediator of oleate- and linoleate- stimulated proliferation of the human breast cancer cell line, MCF-7. GPR40 has a calculated mass of 31.4 kDa bases on its amino acid sequence.