2-Arachidonoyl glycerol-d5 (2-AG-d5) contains five deuterium atoms at the 1, 1, 2, 3, and 3 positions of the glycerol moiety. It is intended for use as an internal standard for the quantification of 2-AG by GC- or LC-mass spectrometry. 2-Arachidonoyl glycerol (2-AG) is an endogenous agonist of the CB1 receptor. Unlike anandamide, 2-AG is present at relatively high levels in the central nervous system, it is the most abundant molecular species of monoacylglycerol found in rat brain. Formation of 2-AG is calcium-dependent and is mediated by the activities of PLC and DAG lipase. 2-AG acts as a full agonist at the CB1 receptor. At a concentration of 0.3 nM, 2-AG induces a rapid, transient increase in intracellular free calcium in NG108-15 neuroblastoma X glioma cells through a CB1 receptor-dependent mechanism. 2-AG is metabolized in vitro by MAG lipase and fatty acid amide hydrolase, with MAG lipase likely being the principle metabolizing enzyme in vivo.