Background: It was demonstrated that ultraviolet(UV) B light induces the release of IL-la in cultured human epithelial cell line and augmentation of GM-CSF production by UVB is reported to be mediated by IL-la in the murine keratinocyte cell line Pam 212. Objective: The purpose of this study was to evaluate the effects of UVB on kinetic profile of IL-1 and GM-CSF mRNA expression and to see whether synthesis of GM-CSF by UVB can be completely inhibited by blocking IL-la mediated pathway. Method: We used a competitive RT-PCR for measuring cytokine gene expression in epithelial cell line after UV radiation. Results: The IL-la mRNA increased as early as 1h after UV irradiation, and then decreased at 3h after the irradiation. Thereafter, the response of IL-la mRNA was upregulated with a second peak at 6h after the UV irradiation. However, mRNA for GM-CSF increased at 1h after UV light exposure and anti-IL-la antibodies could only partially inhibit UV-augmented GM- CSF production. Conclusion: UVB induced GM-CSF production seemed to be mainly mediated by UVB induced IL-la but these results suggest that UVB may also induce GM-CSF production through an IL-la independent pathway. (Ann Dermatol 9:(4):246-252, 1997).