Phosphatidylethanol (PEth) is formed primarily by transphosphatidylation of phosphatidylcholine (PC) by phosphlipase D. Most PEth (about 75%) is incorporated into erythrocyte membranes, and is one of the longest-lived circulating EtOH metabolite yet identified. 1-Palmitoyl-2-linoleoyl-sn-glycero-3-phosphoethanol-d5 (d5-PLPEth) has a fully deuterated ethanol headgroup and can be used as a mass spectrometry standard.