We investigated, by Northern blotting, ELISA, and a chemotaxis assay, the expression of IL-8 mRNA, the production of IL-8 protein, and the biological activity of mononuclear cells (MNC), polymorphonuclear neutrophils (PMN) and plasma, respectively, from patients with Kawasaki disease (KD) who received intravenous immunoglobulin (IVIG). IL-8 mRNA expression by MNC and PMN, the level of IL-8 protein, and the neutrophil chemoattractant activity within plasma were all increased in the acute phase of KD, and were significantly elevated following IVIG therapy. The level of chemotactic activity of neutrophils, but not that of monocytes, in response to F-met-leu-phe was decreased in patients with KD after IVIG. The increased expression of IL-8 in PMN and MNC, the increased plasma level of IL-8 and the decreased level of neutrophil chemotactic activity of the patients who received IVIG therapy might inhibit the accumulation of neutrophils at the sites of inflammation, and may thus reduce the risk of aneurysm formation.