Leukotrienes (Leukotriene) are biologically active compounds synthesized in cells from arachidonic acid by 5-lipoxygenase. Six classes of leukotrienes are involved in bronchial asthma and allergic reactions: LTA4, LTB4, LTC4, LTD4, LTE4, and LTF4. LTB4, in particular, has been measured biochemically because it is a target for labeling in learning the functions of inflammatory response.