Leukotriene B4 is a pro-inflammatory mediator synthesised in myeloid cells from arachidonic acid. Synthesis is catalysed by 5-lipoxygenase and leukotriene A4 hydrolase and is increased by inflammatory mediators including endotoxin, complement fragments, tumor necrosis factor and interleukins. A nuclear membrane protein, 5-lipoxygenase activating protein, is an essential co-factor for 5-lipoxygenase. Leukotriene B4 induces recruitment and activation of neutrophils, monocytes and eosinophils. It also stimulates the production of a number of proinflammatory cytokines and mediators indicating an ability to augment and prolong tissue inflammation. Elevated levels of leukotriene B4 have been found in a number of inflammatory diseases and levels are related to disease activity in some of these. Initial data from pharmacological inhibition studies support a role for leukotriene B4 in the pathogenesis of neutrophil mediated tissue damage, and treatments which reduce its production or block its effects may prove beneficial in neutrophil mediated inflammatory diseases.