Chronic myeloid leukemia (CML) is a clonal disorder of the stem cells which has impaired cell-mediated immune response. Such immune dysfunction may be due to reduced expression of the T-cell receptor (TCR) zeta chain, which is an important component in TCR-mediated signal transduction. In this study, the TCR zeta expression level was detected using a real-time polymerase chain reaction with SYBR Green I technique and relative quantification method. We demonstrated that peripheral blood mononuclear cells (PBMCs) from patients with CML in chronic phase (CML-CP) and CML in complete remission (CML-CR) expressed decreased TCR zeta mRNA levels compared to healthy controls. In addition, TCR zeta chain gene expression was down-regulated in CD4+ T cells from patients with CML-CP. However, the mRNA expression level of the same gene in CD8+ T cells between CML patients and normal individuals did not differ. To confirm that this abnormal zeta chain expression could be corrected, we then stimulated the PBMCs of there patients with interleukin-2, phytohaemagglutinin and concanavalin A. The results showed that it was possible to partially up-regulate zeta chain expression. Taken together, these results indicate that TCR zeta chain expression was decreased in PBMCs and CD4+ T cells from patients with CML and this could be up-regulated partially by using stimulators.