Abstract: Objective: To explore the value of LUNX gene assay in pleural fluid in diagnosis of pleural metastasis of lung cancer.Methods: The LUNX mRNA of 44 pleural effusion samples of lung cancer,13 pleural effusion samples of the tumor excluding lung tissue and 57 pleural effusion samples of benign disease were detected by real-time RT-PCR.All the pleural effusion samples of lung cancer,CEA,CA125,and CYFRA21-1 were tested simultaneously by radioimmunoassay and detected by exfoliative cytology.Results: The positive rate and meso-copies of LUNX gene in lung cancer were 88.6% and 23.58 copies/ml;the positive rate and meso-copies of LUNX gene in benign disease of lung were 5.26% and 0 copies/ml;the positive rate and copies of LUNX gene in tumor and benign disease excluding lung tissue were 0.The sensitivity of LUNX mRNA(88.6%) was significantly higher than that of CEA,CA125 or CYFRA21-1(40.9%,59.1%,61.3%) (P<0.05-P<0.005).Conclusions: LUNX mRNA is a specific molecular marker for diagnosis of pleural metastasis of lung cancer.It has reference value in differential diagnosis of pleural effusion.