The proposed studies will chracterize the structure and function of Platelet Activating Factor (PAF). PAF will be prepared from IgE sensitized rabbit basophils and purified by sequential silicic acid chromotography and thin layer chromotography. This purified material then will be analyzed by mass spectroscopy. Attempts will be made to radiolabel PAF through radiolabelled lipid precursors. The functional activities of PAF for stimulating rabbit and human platelets will be characterized. Human basophils will be obtained and assessed for their ability to produce and secrete PAF; also the cell type in human blood mononuclear cells that produces PAF following stimulation will be identified. It is hoped that the research will elucidate the origin(s) and mode of production of PAF and help to explain the role of this chemical, lipid mediator in the pathogenesis of acute inflammation and tissue injury.