ABSTRACT—The DNA binding activity of the transcription factor, NF‐&kgr;B, is regulated by the phosphorylation and degradation of its inhibitory protein, I&kgr;B, and post‐translational modification involving redox reaction of a cysteine residue (Cys62) of NF‐&kgr;B. We addressed the role of the redox state of endothelial cells in modulating TNF&agr;‐induced NF‐&kgr;B activity. The effects of TNF&agr; on DNA‐binding activity of NF‐&kgr;B and expression of mRNA encoding ICAM‐1 (an NF‐&kgr;B‐activated gene) were studied in human pulmonary artery endothelial (HPAE) cells under basal conditions and after decreasing the intracellular glutathione (GSH) concentration. HPAE cells were treated with buthionine sulfoximine (BSO) (16 h), an inhibitor of GSH synthesis, which caused concentration‐dependent decreases in GSH concentration. Stimulation of control cells with TNF&agr; resulted in reactive oxygen species (ROS) generation and activation of NF‐&kgr;B binding to the ICAM‐1 promoter and ICAM‐1 transcription. However, stimulation of GSH‐depleted cells with TNF&agr; resulted in ROS accumulation secondary to the decreased ROS buffering capacity, and marked impairment of NF‐&kgr;B‐binding activity and ICAM‐1 mRNA expression. Exposure of BSO‐treated cells to the reducing agent dithiothreitol (DTT) before TNF&agr; treatment or supplementation of nuclear extract (isolated after TNF&agr; challenge of BSO‐treated cells) with DTT significantly augmented the effect of TNF&agr; on NF‐&kgr;B‐binding activity and ICAM‐1 mRNA expression. Thus the oxidative modification of NF‐&kgr;B secondary to the loss of ROS buffering capacity may regulate NF‐&kgr;B binding to ICAM‐1 promoter, and thereby ICAM‐1 transcription in endothelial cells.