In the present study we investigated the effect of interleukin-18 (IL-18) on the production of interleukin-1beta (IL-1beta) and soluble interleukin-1 receptor II (sIL-lRII) by human neutrophils. The results obtained indicate that recombinant human interleukin-18 (rhIL-18) induces IL-l beta and, to a lesser extent, sIL-1RII production by human neutrophil isolated from peripheral blood. However, this effect was less important than lipopolysaccharide (LPS) stimulation. Additionally, our observations suggest that IL-18 can induce priming of neutrophils for IL-l beta and, to a lesser extent, sIL-lRII production by LPS--stimulated cells. The ability of IL-18 to serve as an effective modulator for IL-l betaand its regulatory protein may have significance in the inflammatory and immune reactions mediated by IL-l beta.