There is much evidence to support the theory that keratino-cytes and dermal fibroblasts actively participate in inflammatory reactions by the production of proinflamrnatory mediators or cytokines. We investigated the neutrophil chemotactic activity in conditioned media of cultured epidermal cells and dermal fibroblasts, and found that an epidermal cell-derived factor induced fibroblasts to produce a neutrophil chemotactic factor. This neutrophil chemotactic factor was identified as interleukin-8 (IL-8) by the elution position on HPLC and by a neutralization test that uses monoclonal anti-IL-8 antibody (14E4). The epidermal cell-derived factor was fractionated together with thymocyte-proliferating activity on Sephadex G-75 gel chromatography followed by HPLC. It was blocked specifically by anti-interleukin-1 (IL-1) α antibody, which indicates that this factor was IL-1α. Since a variety of inflammatory dermatoses is characterized by the infiltration of neutro-phils into the skin, induction of IL-8 production in fibroblasts by epidermal cells may play an important role in inflammatory skin diseases.