We demonstrated recently that constitutive expression of proinflammatory cytokines interleukin (IL)-1α, IL-6, IL-8, and granulocyte- macrophage colony-stimulating factor in head and neck squamous cell carcinoma is correlated with activation of transcription factor nuclear factor (NF)-κB/Rel A (p50/p65), which binds the promoter region within each of the genes encoding this repertoire of cytokines. NF-κB can be activated after signal-dependent phosphorylation and degradation of inhibitor-κBα and has been reported to promote cell survival and growth. In the present study, we expressed a phosphorylation site mutant of inhibitor-κBα (IκBαM) in head and neck squamous cell carcinoma lines UM-SCC-9, -11B, and -38 to determine the effect of inhibition of NF-κB on cytokine expression, cell survival in vitro, and growth in vivo. After transfection with IκBαM, only a few UM-SCC-9 clones were obtained that stably expressed the mutant IκB, suggesting that expression of a mutant IκBα may affect survival of the transfected UM-SCC cell lines. After cotransfection of IκBαM with a Lac-Z reporter, we found that the number of surviving β-galactosidase-positive cells in the three cell lines was reduced by 70–90% when compared with controls transfected with vector lacking the insert. In UM-SCC-9 cells that stably expressed IκBαM, inhibition of constitutive and tumor necrosis factor-α induced NF-κB activation, and production of all four cytokines was observed. Although UM-SCC-9 IκBαM-transfected cells proliferated at the same rate as vector-transfected cells in vitro, a significant reduction in growth of tumor xenografts was observed in SCID mice in vivo. The decreased growth of UM-SCC-9 IκBαM-transfected tumor cells accompanied decreased immunohistochemical detection of the activated form of NF-κB in situ. These results provide evidence that NF-κB and IκBα play an important role in survival, constitutive and inducible expression of proinflammatory cytokines, and growth of squamous cell carcinoma. NF-κB could serve as a potential target for therapeutic intervention against cytokine and other immediate-early gene responses that contribute to the survival, growth, and pathogenesis of these cancers.