Lipoxins are derived from the oxygenation products of arachidonic acid in human leukocytes. They have exhibited selective biological effects different from those of other eicosanoids. We have examined the effect of lipoxin A4 and B4 (LXA4, LXB4) on the production of leukotriene B4 (LTB4) in human neutrophils. Cultured human polymorphonuclear leukocytes were preincubated with LXA and B and their ability to inhibit LTB4 generation was assessed after incubation with calcium ionophore A23187. We found that the pretreatment of neutrophils with lipoxins inhibit the release of LTB4 by A23187 stimulated PMNs. Our data suggests that LXA4 and B4 can contribute to immunosuppression in an inflammatory state via the inhibition of LTB4 synthesis.