Interleukin (IL)-8 is a member of the supergene family of proinflammatory and chemotactic cytokines recently termed chemokines. IL-8 has been implicated in the pathogenesis of inflammatory skin diseases such as psoriasis. In this study, IL-8 mRNA expression and protein production were determined in normal cultured human epidermal keratinocytes after ultraviolet-B (UVB) irradiation. Messenger RNA levels were determined by the reverse transcriptase-polymerase chain reaction (RT-PCR) method. Total RNA was extracted from cultured keratinocytes at various time points post-irradiation, reverse transcribed to cDNA, and amplified by PCR using a labeled specific primer for the target gene. Amplified products were sized by electrophoresis, visualized by autoradiography, and quantitated by densitometry. Autoradiographs were normalized relative to glyceraldehyde-3-phosphate-dehydrogenase (G3PDH) signals. Constitutive expression of IL-8 mRNA was seen in normal cultured keratinocytes. After 100 or 300 J/m2 UVB irradiation, a rapid increase in IL-8 mRNA level was observed within 1 h after irradiation. At 24 h after irradiation, the mRNA level was elevated 11-13 times compared with the control level. Production of IL-8 protein in culture supernatants was assayed by enzyme-linked immunosorbent assay (ELISA). Significant levels of IL-8 protein were observed at 24 h after irradiation. Cycloheximide treatment blocked this IL-8 protein induction. As IL-8 is known to be an inflammatory cell chemotactic factor, these results suggest a possible role for IL-8 in UVB-induced skin inflammation and diseases.