Abstract: Objective To determine the significance of MDR-1 and MRP mRNA expression in peripheral blood lymphocytes in lung cancer patients with chemotherapy treatment.Methods Peripheral blood samples were taken from each lung cancer patient before chemotherapy and three weeks after the first chemotherapy cycle.The expressions of MDR-1 and MRP were tested for 39 lung cancer cases using RT-PCR technique comparing to 20 normal control cases.Results There was no significant difference for MDR-1 mRNA and MRP mRNA existing in lung cancer cases and control group(P＞0.05).MDR-1 and MRP mRNA expressions were increased after treatment of chemotherapy courses in almost all pathological types of lung cancer.Furthermore,the expression level in small cell lung cancer after chemotherapy was significantly higher than that before.Conclusion Chemotherapy may induce the incidence rate of MDR-1mRNA and MRP mRNA expression in lung cancer.Adenocarcinoma and squamous cell carcinoma are mainly intrinsic MDR while small cell lung cancer is mainly acquired MDR to chemotherapy.Based on thepositive expression rate of MDR-1 mRNA and MRP mRNA in peripheral blood,we may evaluate the results of chemotherapy in lung cancer patients easily and conveniently.