Bronchial asthma is a disease with many unsolved problems and despite an increased availabili ty of anti-asthma drugs, morbidi ty and mortality from this disease are not improving. It is now recognized that asthma should be considered as a chronic inflammatory disease of the lung resulting in bronchial hyperreactivity and subsequent symptoms. The mechanisms underlying airways inflammation and bronchial hyperreactivity have now become a focal point of research in the quest for knowledge about how the management of this disease can be improved. Platelet activating factor (PAF-acether AGEPC) is a naturally occurring ether-linked phospholipid discovered in 1972 associated with IgE mediated allergic responses which has potent effects on platelet activation. PAF is now recognized as a molecule having a diverse range of biological effects relevant to allergic inflammation and asthma including the abili ty to induce long lasting airway inflammation and associated increases in bronchial reactivity. Certain activities of PAF are known to be secondary to platelets activation raising the possibility that this blood element plays a role in the pathogenesis of asthma.