“Platelet activating factor”(PAF) was coined in 1972 by Benveniste and collaborators’ as the name of a substance that was released from basophils after IgE stimulation. Various stimuli also cause other cell types such as platelets, macrophages, and neutrophils to release PAF (for references see review articles cited at the end of this section). The lipid character of PAF was documented in several report^.'^ However, it was not until October of 1979 that Hanahan, Pinckard, and Demopoulos5 published a paper that demonstrated a semi-synthetic preparation of l-alkyl-2-acetyl-sn-glycero-3-phosphocholine (1-alkyl-2-acetyl-GPC) had biological, chemical, and chromatographic prop-* l-Alkyl-2-acetyl-GPC or PAF (platelet activating factor) as used in this report refers to the lipid class l-alkyl-2-acetyl-sn-glycero-3-phosphocholine; the nature of the 0-alkyl moiety is unspecified, but generally it is a saturated (sometimes monoenoic) chain consisting of 16 or 18 carbon atoms. Acyl substituted for acetyl indicates the presence of an esterified long chain fatty acid at the sn-2 position of the glycerol moiety of the lipid. This review covers literature through August of 1983.