OBJECTIVE CD4+CD25+ T regulatory (Treg) cells are a population of T cells which suppress an overactive immune system. CCR4 is a chemokine receptor involved in the recruitment of lymphocytes. Nasopharyngeal carcinoma (NPC) is resistant to immunosurveillance, owing to the increased number of tumor-infiltrating Treg cells which are recruited to the tumor by CCR4.METHODS The percentage of CD4+CD25+Treg cells and CCR4+ cells in tissue or peripheral blood (PB) lymphocytes of patients with untreated NPC or normal subjects was analysed by flow cytometry. RESULTS In both tissue and PB lymphocytes, the percentage of CD4+CD25+ Treg cells and CCR4+ cells was significantly elevated in patients with NPC in comparison with that in the normal tissue of controls. Furthermore, in the patients with NPC, a higher percentage of CD4+CD25+ Treg cells was found in the tumor-infiltrating (T1) lymphocyte population than in the PB population. In the NPC patient group, a general trend towards an increased percentage of Tl Treg cells was found in the patients with advanced stage NPC. The number of CD4+CD25+ Treg cells was positively related to the number of CCR4+ cells in the tumor and in the PB of the patients with NPC, while the number of CD4+CD25+ Treg cells was negatively related to the number of CD4+CD25- T cells.CONCLUSION Immunosuppression was observed in NPC, especially at the tumor sites. CD4+CD25+ Treg cells may suppress CD4+CD25- T cells. CCR4 may have an important role in the recruitment of CD4+CD25+ Treg cells to tumor sites, thus causing resistance to immunosurveillance.