Exposure of human keratinocytes to WA radiation induced an increase in ceramide (CER) intracellular content, with a dose-dependent effect within the range of 4-9 J/cm(2), The production of CER reached a maximum 2 h after WA irradiation, The increase of CER was proportional to the intracellular content of reactive oxygen species, was prevented by the antioxidant vitamin E, and enhanced by the prooxidant buthionine-sulfoximine, suggesting the involvement of an oxidative stress. WA decreased both neutral and acid sghingomyelinase activities measured in vitro, A direct cleavage of sphingomyelin to CER by WA, recently described, was not observed under our experimental conditions. We also show that, downstream of CER, WA activated the Ser/Thr kinases ERK, JNK, and p38, Since ceramide has been shown to play a role in stress kinase activation, our results provide a possible mechanism for WA-induced activation of stress kinases via ceramide formation. However, the actual mechanisms whereby CER is produced in cultured cells under WA exposure remain to be specified,