BAF180 encoding a subunit of the human SWI/SNF chromatin remodeling complex maps to 3p21, in a region where frequent allele loss has been detected in lung cancer. BAF180 can be mutated and has tumor suppressing properties in breast cancer. In addition, another member of this complex, hSNF5/INI1, is a known tumor suppressor gene (TSG) for malignant rhabdoid and childhood central nervous system tumors. Thus, BAF180 is a strong candidate TSG for lung cancer. The objective of this study was to determine whether BAF180 mRNA or protein expression was inactivated or abnormal in lung cancers to prompt detailed DNA promoter methylation or mutational analyses. In 30 non-small-cell and 26 small-cell lung cancer cell lines, most of which had 3p21 allele loss, BAF180 mRNA and protein expression were evaluated by RT-PCR using three sets of primers and Western blotting using two anti-BAF180 antibodies. In all cases, BAF180 was expressed and no abnormal size BAF180 protein was detected. Finally, we found no amino-acid sequence coding mutations in five non-small-cell and five small-cell lung cancer cell lines, while we did find a new splicing isoform of BAF180 (AY281068). We conclude that abnormalities of BAF180 are not frequently involved in the pathogenesis of lung cancer.