1. In the present study, we demonstrate that leukotriene B4 (LTB4) has the ability to activate the human neutrophil 5-lipoxygenase (5-LO). 2. Stimulation of neutrophils with 30 nM 14,15-dideuterio-LTB4 (D2-LTB4) failed to induce the synthesis of LTB4 from endogenous arachidonic acid (AA), but stimulated the formation of LTB4 from 3.3 microM exogenous AA, as determined by GC-MS analysis. 3. The stimulatory effect of LTB4 on 5-LO activity was further examined with an alternative substrate; LTB4 time- and dose-dependently stimulated the 5-LO-mediated conversion of exogenous 15(S)-hydroperoxy-5,8,11,13-(Z,Z,Z,E)-eicosatetraenoate (15-HpETE) into 5(S),15(S)-dihydroxy-6,8,11,13,-(E,Z,Z,E)-eicosatetraenoate (5,15-DiHETE), with a threshold effect at 300 pM. 4. The ability of LTB4 to activate the 5-LO showed structural specificity, since LTB4 was found to be 100 times more potent than omega-hydroxy-LTB4, and 300 times more potent than its delta 6-trans-12-epi-isomer. 5. The LTB4-induced 5-LO activation was effectively inhibited by MK-886 (an inhibitor of 5-LO translocation), by pertussis toxin, and by the LTB4 receptor antagonist, LY-223982. 6. These results demonstrate that the binding of LTB4 to its cell-surface receptor results in 5-LO activation in a process mediated by pertussis toxin-sensitive guanine nucleotide-binding proteins. Our data also suggest that the underlying mechanism involves a translocation of the 5-LO to the membrane. These findings raise the possibility that LTB4 produced by phagocytes may positively feedback on its own synthesis.