NF-kappa B is a pleiotropic transcription factor which controls the expression of many genes and viruses. To date, there is good evidence, but no definitive proof, for its role in tumor formation and development of metastasis. To investigate the possibility that members of the NF-kappa B family could participate in the molecular control of the transformed and invasive phenotype, we examined the expression of these proteins in a variety of human tumor cell lines. The expression of p50, p65, p52 and I kappa B was quantified at the protein level using western immunoblot and mobility shift assay and at the RNA level by northern blot. We observed high expression of the NF-kappa B inhibitor I kappa B in the ovarian carcinoma cell line OVCAR-3 together with constitutive nuclear NF-kappa B activity. We also studied the colon carcinoma cell line HT-29 and its metastatic counterpart HTM-29 and we observed specific expression of the p52 NF-kappa B-related protein in the metastatic cells. Our data confirm that NF-kappa B could be involved in the genesis of a variety of cancers including solid tumors and provide us with interesting models to explore the exact role of these transcription factors in cancer.