To evaluate the expressions of CD4(+) CD25(high)CD127(low/-) regulatory T cells (Tregs) in peripheral blood from patients with transitional cell carcinoma (TCC) in urinary system, we investigated the proportion of Treg population in CD4(+) T from 93 patients with TCC, 38 with benign urinary diseases, and 37 healthy subjects by using flow cytometric analysis and analyzing different clinicopathologic characteristics and the changes before and after operation. We found that the proportion of Treg in peripheral blood from patients with TCC was significantly increased as compared with the other two groups. There was a strong correlation between the proportion of Treg and tumor recurrence, quantity, lymph node metastasis (P<0.01), as well as pathological stage; no correlation was found between the proportion of Treg and clinical TNM stage (P>0.05). The proportion of Treg was also different before and after operation (P<0.05). This suggest that CD4(+)CD25(+)CD127(low/-) regulatory T cells may be responsible for immune suppression in TCC patients. The resection of tumor can decrease the proportion of Treg in peripheral blood. J. Clin. Lab. Anal. 23:197-201, 2009. (C) 2009 Wiley-Liss, Inc.