NF‐κB is a dimeric transcription factor that is involved in the regulation of a large number of genes that control various aspects of the immune and inflammatory response. It is activated by a variety of stimuli ranging from cytokines, to various forms of radiation, to oxidative stress (such as exposure to H₂O₂). Recent studies have advanced our understanding of the signal transduction pathway leading to NF‐κB activation by cytokines and will provide insights for the mechanism by which NF‐κB is regulated by oxidative stress. An important question that is yet to be answered is whether reactive oxygen species play a physiological role in NF‐κB activation.—Li, N., Karin, M. Is NF‐κB the sensor of oxidative stress? FASEB J. 13, 1137–1143 (1999)