Among agents which activate platelets PAF is unique since it is the only phospholipid known to date which stimulates platelets at nanomolar range. The first indications of such a mediator dates back to 1966 when it was observed that a mixture of rabbit platelets and stimulated leukocytes released histamine on specific antigen challenge (Barbaro and Zvaifler, 1966). In 1971 it was observed that a A fluid phase mediator was released from leukocytes of Ig E sensitized rabbits. This mediator activated platelets releasing vasoactive amines (Henson, 1970). Subsequently, two groups independently confirmed these observations (Sirganian and Osler, 1971; Benveniste et. al. 1972) and the soluble factor was named ‘platelet activating factor, PAF (Benveniste et. al. 1972). These initial observations led to research on chemical identification of PAF. In 1979 three groups of investigators independently contributed towards the structural identification of PAF (Demopoulos et. al. 1979; Benveniste et. al., 1979; Blank et. al. 1979).