CD4+ CD25+ regulatory T cells have been shown to maintain peripheral tolerance against self and foreign antigens. In this study we analyzed the effect of circulating CD4+ CD25+ T cells on CD8+-T-cell responses of patients with chronic and resolved hepatitis B virus (HBV) infection. We demonstrated that circulating CD4+ CD25+ T cells modulate the function and expansion of HBV-specific CD8+ cells ex vivo in all patients, regardless of whether they have chronic or resolved HBV infection. The possible role of CD4+ CD25+ T cells in the pathogenesis of chronic HBV infection is not supported by these data. However, these results might have implications for optimizing future immunotherapeutic approaches to HBV treatment.