We have examined the in vitro effects of two recombinant human monokines, interleukin-1 alpha (rHuIL-1 alpha) and tumor necrosis factor alpha (rHuTNF alpha), on bovine neutrophil functions. Both rHuIL-1 alpha (10 to 1,000 ng/ml) and rHuTNF alpha (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 rHuIL-1 alpha (1 to 1,000 ng/ml) and rHuTNF alpha (0.5 to 50 ng/ml) primed bovine neutrophils for an enhanced oxidative burst to subsequent stimulation with opsonized zymosan. Neutrophils pre-treated 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 rHuIL-1 alpha (10 and 100 ng/ml) and rHuTNF alpha (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 rHuIL-1 alpha or rHuTNF alpha, further augmented the maximal oxidative response of neutrophils stimulated with opsonized zymosan. Bovine neutrophils released both primary and secondary granules in response to rHuIL-1 alpha and rHuTNF alpha, and also exhibited enhanced adherence in the presence of either monokine.