Purpose: We have previously identified mouse Tarsh as one of the cellular senescence-related genes and showed the loss of expression of TARSH mRNA in four human lung cancer cell lines. TARSH is a presumptive signal transduction molecule interacting with NESH, which is implicated to have some roles in lung cancer metastasis. Methods: The amplification of complete ORF-encoding TARSH cDNA was done with reverse transcription-PCR. Northern blotting was carried out using TARSH cDNA probes. To clarify the relationship between TARSH and lung cancer, we quantified TARSH mRNA expression in 15 human lung cancer cell lines and 32 primary non-small cell lung cancers. Results: We first determined the complete ORF-encoding cDNA sequence which is expressed in the human lung. On the Northern hybridization analysis, TARSH was strongly expressed in the human lung. The expression of TARSH mRNA is remarkably downregulated in all the lung cancer cell lines examined. Furthermore, TARSH expression was significantly low in all of the tumor specimens when compared to the expression in corresponding non-neoplastic lung tissue specimens. Conclusion: The cancer-associated transcriptional inactivation of TARSH suggests that TARSH could be used as a biomarker for lung cancer development as well as a molecular adjunct for lung carcinogenesis in human.