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AIM: Activation of transcription factor nuclear factor-κB (NF-κB) has been shown to play a role in cell proliferation,apoptosis, cytokine production, and oncogenesis. The purpose of this study was to determine whether NF-κB was constitutively activated in human colorectal tumor tissues and, if so, to determine the role of NF-κB in colorectal tumorigenesis, and furthermore, to determine the association of RelA expression with tumor cell apoptosis and the expression of Bcl-2 and Bcl-xL.METHODS: Paraffin sections of normal epithelial, adenomatous and adenocarcinoma tissues were analysed immunohistochemically for expression of RelA, Bcl-2 and Bcl-xL proteins.Electrophoretic mobility shift assay (EMSA) was used to confirm the increased nuclear translocation of RelA in colorectal tumor tissues. The mRNA expressions of Bcl-2 and Bcl-xL were determined by reverse transcription polymerase chain reaction (RT-PCR) analysis. Apoptotic cells were detected by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate fluorescence nick end labeling (TUNEL) method.RESULTS: The activity of NF-κB was significantly higher in adenocarcinoma tissue in comparison with that in adenomatous and normal epithelial tissues. The apoptotic index (AI)significantly decreased in the transition from adenoma to adenocarcinoma. Meanwhile, the expressions of Bcl-2 and Bcl-xL protein and their mRNAs were significantly higher in adenocarcinoma tissues than that in adenomatous and normal epithelial tissues.CONCLUSION: NF-κB may inhibit apoptosis via enhancing the expression of the apoptosis genes Bcl-2 and BCl-xL. And the increased expression of RelA/nuclear factor-κB plays an important rote in the pathogenesis of colorectal carcinoma.