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Cytokines such as IL-1 or TNF-alpha induce a specific cellular responses through the activation of a transcriptional factor, NF kappa B. This activation requires the phosphorylation of an inhibitory subunit, I kappa B, which relies upon an intracellular production of reactive oxygen intermediates. Peroxides, but also the increase of the GSSG/GSH ratio are assumed to play a major role in this process. There is presently a good agreement on the overall scheme of IL-1 and TNF-alpha activation and on the involvement of reactive oxygen intermediates in the corresponding signal transduction cascades. However several questions regarding the molecular mechanisms involved in particular steps of these cascades remain largely unresolved: how and at which subcellular level, do the cells produce these reactive oxygen intermediates that will contribute to NF kappa B activation in response to IL-1 or TNF-alpha? What are the kinases/phosphatases, being modulated by peroxides and what is the contribution of high GSSG levels to NF kappa B activation? In this paper, we will briefly overview this basic issue in cell biology and highlight some of the recent experimental data that will help us to understand the exact role of reactive oxygen intermediates in NF kappa B activation and the molecular mechanisms involved.