Abstract: Objective To investigate the relationship between the expression of pro-gastrin-releasing peptide(ProGRP) mRNA in peripheral blood and serum ProGRP protein and their association with pathological factors and chemotherapy response in patients with small cell lung cancer(SCLC). Methods The expression of ProGRP mRNA was detected by real-time reverse transcriptase-polymerase chain reaction (RT-PCR) in peripheral blood from 61 patients with SCLC before the first and the third chemotherapy. Serum ProGRP protein was also determined by enzyme linked immunosorbent assay (ELISA). Results ProGRP mRNA expression and the level of serum ProGRP protein were related to primary tumor size, clinical stages and distant metastasis(P<0.05). Linear correlation analysis revealed then there was a correlation between ProGRP mRNA expression in peripheral blood and serum ProGRP protein level (R²=0.34, P<0.05). Both levels of ProGRP mRNA and serum ProGRP protein in PR and CR cases were signifi cantly declined following the second cycle of chemotherapy (P<0.05). There was no obvious decrease in SD and PD cases before or after treatment (P>0.05). Conclusion ProGRP mRNA could be used as a marker in the detection of circulating tumor cells in SCLC, and regular quantifi cation of ProGRP mRNA in peripheral blood may be useful to evaluate the therapeutic effi ciency and predict prognosis of SCLC patients. Serum ProGRP may also serve as a prognostic marker and be used in the assessment of therapeutic response in SCLC patients and the method is simple and feasible.