Activity of the transcription factor nuclear factor-κB (NF-κB) has been shown to be necessary for maintaining neuronal viability. In cultured rat cerebellar granule neurons, trophic factor withdrawal induces NF-κB inactivation, resulting in cell death. The exact mechanism of this inactivation, however, has not been revealed. Here we report that trophic factor deprivation in cultured cerebellar granule neurons leads to a rapid and sustained increase in the level of IκBα and IκBβ, the inhibitory proteins of NF-κB, causing prolonged NF-κB inactivation. Transient NF-κB activation resulting in new IκBα mRNA and protein synthesis gives rise to the rapid increase of IκBα level. The importance of elevated IκB level in neuronal apoptosis was confirmed in transfection experiments. Ectopic expression of a stabilized form of IκBα protein promoted neuronal death. Our findings suggest a novel mode of initiation of neuronal apoptosis wherein survival signal withdrawal induces NF-κB to lethally turn itself off.