Natural or recombinant neutrophil activating cytokine (IL-8) induced migration across polycarbonate filters of human A 2058 melanoma cells. Anti-IL-8 antibodies blocked IL-8 induced melanoma cell migration. Checkerboard experiments revealed a gradient-dependent response of A2058 melanoma cells to IL-8. Filters exposed to IL-8 and washed supported melanoma cell migration, thus implying a haptotactic component in the response. The homologous polypeptide platelet factor 4 was inactive. The observation that IL-8 affects melanoma cells emphasizes the need for a comprehensive analysis of the spectrum of action of platelet factor 4-related peptides. The effect of the inflammatory cytokine IL-8 on melanoma cells may be relevant to augmented secondary localization of tumors at sites of inflammation.