We have examined the in vitro effects of two recombinant human monokines, interleukin-1 alpha (rHulL-1α) and tumor necrosis factor alpha (rHuTNFα), on bovine neutrophil functions. Both rHulL-1α (10 to 1,000 ng/ml) and rHuTNFα (5 to 50 ng/ml) directly stimulated the oxidative burst of bovine neutrophils as measured by Luminol-dependent chemiluminescence, superoxide anion generation, and hydrogen peroxide production. In addition, both rHulL-1α (1 to 1,000 ng/ml) and rHuTNFα (0.5 to 50 ng/ml) primed bovine neutrophils for an enhanced oxidative burst to subsequent stimulation with opsonized zymosan. Neutrophils pretreated with either monokine exhibited an earlier, as well as stronger, zymosan-stimulated Luminol-dependent chemiluminescence response, as compared to untreated neutrophils. Exposure of bovine neutrophils to combinations of suboptimal doses of rHulL-1α (10 and 100 ng/ml) and rHuTNFα (0.5 and 5 ng/ml) resulted in a synergistic stimulation of Luminol-dependent chemiluminescence, whereas, no synergism was observed when using optimal doses of each monokine. Pre-incubation of bovine neutrophils with an optimal concentration of recombinant bovine interferon gamma (100 U/ml), and either rHulL-1α or rHuTNFα further augmented the maximal oxidative response of neutrophils stimulated with opsonized zymosan. Bovine neutrophils released both primary and secondary granules in response to rHulL-1α and rHuTNFα, and also exhibited enhanced adherence in the presence of either monokine.