Leukotrienes (LTS) are a novel group of arachidonic acid (A.A.) metabolites which have potent biological actions. These actions suggest that LTS may have a role in various pathological conditions. The chemotactic and chemokinetic actions of LTS suggest that Leukotriene B4 (LTB4) has a role in inflammatory conditions and tissue damage. LTC and LTD cause a change in pulmonary mechanism, including reduction in expiratory flow, tightness of the chest and wheesing suggest that LTS have a role in respiratory diseases. The vasoconstrictor actions of leukotrienes in coronary circulation of many species suggest that they may be involved in myocardial ischaemia, angina and perhaps are generated locally in the coronary vascular bed. From these observations, it will be of great interest to investigate the effects of LT antagonists and lipoxygenase inhibitors in these conditions.