We have examined the effect of UVB and solar-simulated irradiation on the expression of the AP-1 family of transcription factors and the cytokine IL-6 both in cell cultures and in human skin in vivo. UVB irradiation potently induced c-jun, junB and c-fos mRNA levels in vitro in HaCaT cells. IL-6 mRNA was induced in response to UVB irradiation 2-3 h later than c-jun, junB and c-fos mRNAs. In human skin in vivo, solar-simulated irradiation induced transiently junB expression. Genistein, a tyrosine kinase inhibitor, augmented the induction of c-jun and junB by UVB irradiation in HaCaT cells. The results of this study provide evidence that in addition to c-jun and c-fos, junB is also an essential component of the human UV-response. This study also suggests that UVB irradiation regulates the AP-1 family by several mechanisms and that the signalling mechanisms of UVB irradiation are considerably different from the ones used by UVC irradiation.