Abstract: Leukotriene B₄(LTB₄), a biologically active mediator derived from arachidonic acid via 5-lipoxygenase, is a potent chemotactic agent for polymorphonuclear leukocytes and in vivo may participate in inflammatory reactions by inducing leukocytes recruitment and by modulating pain responses. This article reports the inhibitory actions of some anti-inflammatory agents on 5-lipoxygenase, using RP-HPLC for measuring LTB₄. The results indicate that flufenamic acid, a compound known to inhibit the activity of phospholipase A₂ and the biosynthesis of PGs, can inhibit the biosynthesis of LTB₄ as well, but aspirin, indomethacin, piroxicam, hydrocortisone and S-1 did not exhibit this activity.