Prostaglandin E2 (PGE2) is the major eicosanoid product of cyclooxygenase-1 and 2 in epithelial cells, leukocytes, reproductive tissues, and many others. PGE2 contracts smooth muscle, protects the gastric mucosa, modulates immune function, and regulates fertility and implantation. PGE2 acts through at least four 7-transmembrane G-protein coupled receptors, EP1·EP4. PGE2-biotin is an affinity probe which allows PGE2 to be detected through an interaction with the biotin ligand. PGE2-biotin was designed to allow PGE2 to be detected in complexes with transmembrane receptors and/or nucleic acid or protein binding partners. It is thus a tool to be used in the general elucidation of the mechanism of action of PGs.