Interleukin-1 receptor antagonist (IL-1RA) is a cytokine that acts to antagonize IL-1 activity without agonist function. The expression of IL-1RA has been reported in many cell types, including the keratinocyte that covers the outer most part of the skin. However the modulation of IL-1RA by ultraviolet B (UVB), which is the most biologically active UV, has not been reported yet. We therefore selected a keratinocyte cell line with a cytokine-producing profile similar to that of keratinocytes and tested the effect of UVB on its ability to produce IL-1RA mRNA. IL-1RA mRNA was constitutively expressed in the cell line and began to be suppressed by 3 h after the UVB irradiation with 100 mJ/cm2. The level of IL-1RA expression became lowest by 16 h after the irradiation with 100 mJ/cm2. Simultaneously, IL-1 alpha mRNA started to increase by 1 h and peaked by 3-16 h after the irradiation with 10-100 mJ/cm2. The differential expression of IL-1 alpha and IL-1RA mRNA following exposure to a high dose (100 mJ/cm2) of UVB may markedly potentiate the role of IL-1 in UV-induced inflammation.