Abstract: Objective: To measure the amount of CD4⁺ CD25^high regulatory T cells in the circulation of patients with pancreatic carcinoma.Methods: The amount of Treg cells in the peripheral blood of 58 cancer patients and 14 healthy controls was determined by flow cytometry.The phenotype of Treg was also determined by flow cytometry.Results: Compared with healthy controls(2.53±1.26)%,the amount of Treg cells in the peripheral blood of patients with pancreatic carcinoma was increased(15.61±13.97)%(P<0.01).Compared with healthy controls,the proportions of Treg cells in the patients with pancreatic carcinoma in stage Ⅰ-Ⅱ(18.75±20.76)%,stage Ⅲ(13.71±9.53)%,stage Ⅳ(14.20±7.46)%,were significantly higher(P<0.01).In addition,the Treg cells had high expression of CD45 RO combined with low expression of CD45 RA.The costimulatory molecules CD80,and CD86 were not detected on the surface of Treg cells,whereas CD152(CTLA-4) was variably expressed.Some of the Treg cells had surface expression of HLA-DR.The marker of recent activation(CD69) was not found on the surface of Treg cells whereas HLA-Ⅰ was highly expressed on the surface of Treg cells.Conclusions: The amount of Treg cells is increased in the peripheral blood of patients with pancreatic carcinoma.These Treg cells may mitigate the immune response against cancer,and may be related to tumor progress in patients with pancreatic carcinoma.