Leukotriene B4 (LBT4) is a potent primary stimulator of neutrophil chemotaxis, aggregation and degranulation and induces superoxide production at higher concentrations. To determine whether LTB4 modulates neutrophil responses to oxidative stimuli, human neutrophils (PMN) were incubated with LBT4 prior to stimulation with formylmethionylleucylphenylalanine (fMLP, 10-7 mol/l), opsonized zymosan (OZ, 250 .mu.g/ml), or phorbol myristate acetate (PMA, 32 nmol/l). Superoxide (O2-) production by stimulated PMN was assessed by the superoxide dismutase-inhibitable reduction of cytochrome c. LTB4 alone did not stimulate O2- production in concentrations below 10-7 mol/l and had no effect on the O2- assay. In the concentration range of 10-12 to 10-8 mol/l, LTB4 did not alter O2- release induced by OZ or PMA. LTB4-treated cells demonstrated enhanced O2- production following exposure to fMLP, and in the presence of 10 nmol/l LTB4, generated 180% .+-. 41% of O2- quantities produced by control cells (n = 23). Enhancement was LTB4 dose-dependent, was maximal in the range of 1-10 nmol/l LTB4, was not reversed by removal of the lipid from the medium prior to fMLP stimulation, and was not dependent on the presence of Ca2+ or Mg2+ in the suspending medium. Chemiluminescence of fMLP-stimulated neutrophils was increased to 3.23% of controls in neutrophils preincubated with 10 nmol/l LTB4. Unlike augmentation of oxidative responses to fMLP seen with other degranulating stimuli, enhancement by LTB4 was not correlated with an increase in 3H-fMLP receptor binding. In addition to its primary effects on neutrophil function, LTB4 modulates PMN oxidative responses to the chemotactic peptide and, thus, may amplify the release of oxygen metabolites at inflammatory foci.