Abstract： Objective To investigate the changes of proportion and suppression function of CD-4+ CD-25+ regulatory T cells in the peripheral blood of patients with aggressive periodontitis.Methods Flow cytometric analysis was used to detect the frequency of CD-4+ CD-25+ regulatory T cells in the peripheral blood of 16 patients with generalized aggressive periodontitis and 17 patients with chronic periodontitis,as well as 17 periodontal healthy controls.Furthermore,CD-4+ CD-25+ regulatory T cells and CD-4+ CD-25- T cells were separated from peripheral blood of each enrolling subject using magnetic cell sorting technology.The direct suppression effect of CD-4+ CD-25+ regulatory T cells on CD-4+ CD-25- T lymphocytes proliferation was performed by the mixed lymphocytes reaction and measured by 3H-thymidine radioactive assay.Results The patients with generalized aggressive periodontitis had a lower frequency of CD-4+ CD-25+ regulatory T cells(9.71±4.01)%in the peripheral blood than periodontal healthy controls [(14.72±3.51)%]and chronic periodontitis patients[(17.01±5.16 )%],P＜0.05.A significant decrease was found in the suppression function of CD-4+ CD-25+ regulatory T cells from peripheral blood of patients with generalized aggressive periodontitis when co-cultured with CD-4+ CD-25- T lymphocytes in the proportion of 2:1,1:1 and 1:2 as compared with chronic periodontitis patients and periodontal healthy controls(P＜0.05).Conclusions Diminished numbers and decreased suppression function of CD-4+ CD-25+ regulatory T cells were found in patients with generalized aggressive periodontitis.