Interleukin-1 alpha and -1 beta, interleukin-6, and tumor necrosis factor-alpha may have a protective effect against malignant transformation of melanocytes. By using monoclonal and polyclonal antisera we investigated, in paraformaldehyde-fixed tissue, the cellular distribution of these cytokines in human common and dysplastic nevocellular nevi and in malignant melanoma. Generally, the immunolabeling for all of these cytokines was both cytoplasmic and perinuclear as well as present in the basement membrane, which surrounds the individual cells or cellular nests of some of the nevi. In compound and intradermal nevi the immunolabeling was abundant, although there was a variation in the staining intensity between individual cells and even inside a single nevus cell, ranging from weak to strong. There was a strong labeling of the basement membrane around the cellular nests and around individual cells inside or outside the nests in the papillary and reticular dermis. With regard to the common junctional and dysplastic nevi and malignant melanoma, occasional immunolabeling could be seen in some cells within the cellular nests in the junctional area or papillary dermis, ranging from faint to moderate in intensity, but in this case the basement membrane around individual cells or cellular nests was not stained. The staining of nevocellular nevi and malignant melanoma indicates the possibility of these cytokines being synthesized by the nevi and melanoma cells. The labeling of the basement membrane in compound and intradermal nevi suggests that cytokines produced by nevocellular cells may be stored in the basement membrane, from which they could be released upon environmental or mechanical challenge. This distribution pattern would support the hypothesis that these cytokines may protect the common nevi from malignant transformation.