The transcription factor nuclear factor-κB (NF-κB) is sequestered in the cytoplasm by inhibitor of κB (IκB) and activated by two pathways: canonical signalling involves the degradation of IκB by IKKα, IKKβ and NEMO (which together form the IKK complex) followed by the nuclear translocation of the NF-κB dimer; non-canonical signalling is mediated by NIK (NF-κB-inducing kinase)-dependent activation of IKKα, which results in the release of the mature p52 subunit from the NF-κB precursor p100. This study now shows that the basal levels of NIK (which is rapidly degraded in unstimulated cells) were enhanced in NEMO-deficient cells, suggesting that the presence of NEMO usually decreases NIK levels to prevent non-canonical NF-κB signalling. The authors found that an intact and catalytically active IKK complex, as well as NF-κB transcriptional activity, was required to reduce NIK levels. Thus, classic NF-κB signalling suppresses the accumulation of NIK to inhibit basal non-canonical NF-κB signalling.