Phosphaytidylethanol (PEth) is formed primarily by transphosphatidylation of phosphatyidylcholine (PC) by phospholipase 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-arachidonoyl-sn-glycero-3-phosphoethol-d5 (d5-PAPEth) is fully deuterated on the ethanol headgroup and is an analog of one of the five most abundant naturally occurring PEth species.