Abstract: Objective : To observe the influence of chemotherapy on the switch between Th1 and Th2 cytokines in colon carcinoma. Methods : The gene expression of Th1 and Th2 cytokines was detected by reverse transcription polymerase chain reaction (RT-PCR) in 35 normal controls, 30 cases with benign colon polyps and 67 patients with colon carcinoma before and after chemotherapy. Results : Th1 and Th2 cytokines were negative in peripheral blood from those with benign polyps and the normal controls. The mRNA expression of IL-4, IL-6, and IL-10 in PBMCs from patients with colon carcinoma was significantly higher than in patients with benign polyps or the normal controls (P0.05). IFN-γ expression was not detected in any patients (0/67) before treatment, and the detection of IL-2 expression was only 3/67. After chemotherapy, the expression of Th1 and Th2 cytokines in colon carcinoma was significantly changed. There was also a significant enhancement in IFN-γ and IL-2 expression paralleled by a substantial decrease in IL-4, IL-6, and IL-10. Conclusion : The expression of Th1 cytokine was inhibited and there was a concomitant state of Th2 cytokine predominance in PBMCs from patients with colon carcinoma. Chemotherapy can convert the imbalanced state of Th1 and Th2 cytokines present in colon carcinoma and make it incline more toward normal.