Abstract: Objective :To detect the expression of cytokeratin 19 (CK19) mRNA in peripheralblood of patients with non-small cell lung cancer (NSCLC) and to examine the correlation between thisexpression and the clinical stage and pathological type. Methods :The expression of CK19 mRNA inperipheral blood was detected using reverse transcriptase polymerase chain reaction (RT-PCR). Re-Sults :In the NSCLC group,the positive rate of CK19 mRNA in peripheral blood was 60.7%, which wassignificantly higher than the other two groups (P<0.01), and the level increased significantly as the clin-ical stage progressed (P<0.05).The positive rate of CK19 mRNA in different pathological types ofNSCLC showed no significant difference (P>0.05). Conclusion :The detection of CK19 mRNA in pe-ripheral blood is helpful for making a prognosis as well as to select the method of treatment in patientswith NSCLC. The pathological type of NSCLC does not have any influence on CK19 expression.