Leukotriene B4 (LTB4) is a potent lipid proinflammatory mediator. Biosynthesis of LTB4 involves the enzymatic transformation of arachidonic acid by 5-lipoxygenase to form the epoxide intermediate, LTA4, which is then dehydrated by LTA4 hydrolase to yield LTB4. Through binding to its membrane receptors, LTB4 causes leukocyte adhesion and chemotaxis. At higher concentrations, LTB4 induces aggregation, granule enzyme release and superoxide anion generation by neutrophils. The leukocyte-activating effects of LTB4, together with overproduction of LTB4 in certain inflammatory disorders, implicates LTB4 as a lipid proinflammatory mediator.