Platelet-activafing factor (PAF-acether) is a potent mediator of anaphylaxis and inflammation. It induces aggregation of platelets mad releases their vasoactive amines. PAF-acether has' been shown to be produced by basophils [1, 2], macrophages [3, 4], neutrophils [51, and platelets themselves [6]. This mediator, partially characterized as a 2acylglycero-phosphorylcholine (2-acyl-glyceroPC) [7], was fully identified as a 1-O-alkyl-2-Oacetyl-sn-glyceryl-3-PC by synthesis from natural ptasmalogens [8, 9] and by total synthesis of the 1-O-octadecyl-ether 2 (see table I and fig. 1) [101. The structure for natural platelet-activating factor released from antigen stimulated IgE-sensitized basophils was confirmed by Hanahan et al. [11]. Recently, 1-O-alkyl-2-Iyso-glyceryl-3-PC has been isolated from hog leucocytes; this precursor (or