Recent studies have implicated a role for the p50 subunit of the NF-kappa B transcription factor complex in tumorigenesis. Therefore, we investigated the expression of the p50 subunit of the NF-kappa B transcription factor complex in paired normal and non-small cell lung carcinoma (NSCLC) tissues. Here we show that nine of 11 (81.8%) fresh NSCLC tissues expressed from two- to 20-fold higher levels of the p50 subunit than normal lung tissue. Thirteen NSCLC cell lines also exhibited high levels of p50. Alterations in the normal NF-kappa B/rel pathway of regulation may play a role in the genesis of NSCLC.