Although it has been suggested that some biological activities of platelet-activating factor (PAF) are mediated by, at least in part, reactive oxygen intermediates (ROI), the precise mechanisms underlying the interaction between the two remains to be elucidated. Antioxidants, such as α-tocopherol acid succinate, N-acetyl-L-Cysteine, pyrrolidinedithiocarbamate failed to inhibit PAF-induced immediate systemic reactions such as lethality, symptoms of disseminated intravascular coagulation, and histological changes such as pulmonary edema and hemorrhage in renal medullae 10 min following PAF injection. In contrast, antioxidants significantly inhibited both the in vivo and in vitro PAF-induced NF-κB activation and NF-κB-dependent TNF-α expression. The effects of the antioxidants were due to their inhibition of PAF-induced degradation of IκBα, a protein responsible for keeping NF-κB in an inactive form. A protein tyrosine kinase and N-tosyl-L-phenylalanine chloromethyl ketone sensitive serine protease were involved in both PAFand H₂O₂-induced NF-κB activation. Collectively, these data indicate that the PAF-induced NF-κB activation is selectively mediated through the generation of ROI.