OBJECTIVES To identify the characteristics of circulating CD4(+)CD25(high) regulatory T cells in chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS). We sought to discover the possible mechanism underlying induction of CP/CPPS by autoimmune factors. METHODS A total of 69 men with CP/CPPS and 25 age-matched, asymptomatic controls underwent quantification of peripheral blood CD4(+)CD25(high) regulatory T cells, using flow cytometry, followed by measurement of interleukin (IL)-6, IL-10, tumor necrosis factor-alpha (TNF-alpha), and transforming growth factor-beta 1 (TGF beta 1) in serum, and forkhead box P3 (FOXP3) mRNA level in peripheral blood mononuclear cells, using enzyme-linked immunosorbent assay and real-time quantitative reverse transcriptase-polymerase chain reaction, respectively. RESULTS The FOXP3 gene mRNA level in CP/CPPS patients was significantly lower than that in controls. Serum TNF-alpha level increased but the TGF beta 1 level decreased in CP/CPPS patients. No change was observed in the levels of IL-6 and IL-10. However, there was normal frequency of CD4(+)CD25(high) T cells in CP/CPPS patients. No differences were observed in expression of FOXP3 and serum cytokines and population of CD4(+)CD25(high) T cells between CP/CPPS IIIA and IIIB patients. In addition, statistically significant correlation was only found between serum IL-6 production and national institutes of health-chronic prostatitis symptom index total score of CP/CPPS patients. The frequency of CD4(+)CD25(high) T cells and FOXP3 expression level did not correlate with age, duration, and total national institutes of health-chronic prostatitis symptom index score of CP/CPPS patients. CONCLUSIONS FOXP3 and serum cytokines, such as TNF-alpha and TGF beta 1, might be important for the pathogenesis of CP/CPPS and possibly affect the suppressive function of CD4(+)CD25(high) regulatory T cells. This influence may result in the onset of CP/CPPS, but its assessment requires further study. UROLOGY 75: 938-942, 2010. (C) 2010 Elsevier Inc.