The modulatory effects of ultraviolet B (UVB) irradiation on cutaneous inflammatory responses are well known but their mechanism remains obscure. It has been proposed that regulated upon activation normal T-cell expressed and secreted protein (RANTES), which is one of the chemokines produced by epidermal keratinocytes, might play an important role in the pathogenesis of cutaneous inflammatory disorders, such as atopic dermatitis and psoriasis vulgaris. This study was designed to determine whether UVB irradiation could affect the production of RANTES that is induced in cultured normal human epidermal keratinocytes upon stimulation by inflammatory cytokines. We measured levels of the transcript of the gene for RANTES in cultured keratinocytes and of RANTES itself in culture supernatants by semiquantitative reverse transcription and the polymerase chain reaction and by an enzyme-linked immunosorbant assay (ELISA), respectively. Neither the transcript nor RANTES itself was detected without prior stimulation of cells by tumor necrosis factor alpha (TNF-alpha) and/or interferon gamma (IFN-gamma) and production of RANTES was not induced by UVB (100 J/m2) irradiation alone. Cells were irradiated with UVB just before addition of TNF-alpha and IFN-gamma to the medium and then cells and culture supernatants were harvested 12, 24, and 36 h later. In both irradiated and non-irradiated cells, RANTES mRNA was first detected at 12 h and the level increased subsequently. RANTES itself was detected at 24 h, with a higher level at 36 h. At all time points examined, UVB irradiation inhibited the production of RANTES mRNA and of the protein itself. These results suggest that suppression of the production of RANTES by epidermal keratinocytes might be involved in the modulatory effects of UVB irradiation on cutaneous inflammation.