The synthesis is described of two isomeric lysophosphatidylethanolamines, containing the fatty acid residue in the y-and 8-ester position, respectively. The preparation of the (8-stearoyl)-~L-u-lysophosphatidylethanolamine was accomplished by two procedures. According to the first method developed, a silver iodide interchange reaction was carried out between y-0-benzyl-8-stearoylglycerol-a-iodohydrin and silver benzyl 2-phthalimidoethyl phosphate. This procedure was also applied for the synthesis of (y-stearoy1)-DL-a-lysophosphatidylethanolamine by starting from y-stearoyl-8-0-benzylglycerol-u-iodohydrin. A second method involved the preparation of silver benzyl y-0-benzyl-p-stearoylu-glycerol phosphate which was coupled with 2-iodoethylphthalimide. This pathway also furnishes several intermediates which are suitable for the preparation of other types of lysophosphatides. A distinction between both structurally isomeric lysophosphatidyl-ethanolamines by enzymic means proved to be possible. Phospholipase A from snake venom was shown to release the fatty acid constituent from the p-acyl isomer, whereas the y-acyl isomer was not susceptible to the action of this enzyme.Phosphatide mixtures extracted from natural sources have frequently been demonstrated to contain homologues carrying only one fatty acid constituent; such compounds have been denoted as lysophosphatides. Confirming previous observations 2 , the native character of lysolecithins from animal tissues has been recently established 3 . Fresh evidence indicates that naturally occurring lysophosphatides not only result from the catabolism of diacyl-phosphoglycerides, but may play an important part in phosphatide anabolism as well, by acting as substrate for acylating enzymes4.Contribution No 39 in the series: Metabolism and functions of phosphatides. , Rec. trav. chim. 72, 395 (1953). be observed in these experiments between this lecithin and a synthetic one.