It was recently demonstrated that interleukin-8 (IL-8) is produced by cultured melanoma cells and acts as an essential autocrine growth factor. Earlier studies from our laboratory demonstrated a direct correlation between IL-8 expression in human variant cell lines and their metastatic potential in nude mice. In the present study we examined the expression of IL-8 in human malignant melanomas using immunohistochemistry to correlate IL-8 levels with disease stage. None of the radial growth phase (RGP) tumours (melanoma in situ) expressed IL-8. In contrast, 50% of the vertical growth phase (VGP) tumours (invasive melanoma), which have a high risk of metastasis, showed IL-8 immunoreactivity. Further, all the metastatic lesions analysed showed intense staining for IL-8; the levels were higher than those observed in the primary skin tumours. In summary, the data suggest an association between the expression of IL-8 and the metastatic phenotype.