We investigate the frequencies of CD4(+)CD25(+)Foxp3(+) T cells and allergen-specific IL-10(+)IL-4(-), IFN-gamma(+)IL-4(-), IL-4(+)IFN-gamma(-)CD4(+) T cells (which display characteristics of nTreg, Tr1-, Th1- and Th2- cells, respectively) in peripheral blood mononuclear cells (PBMCs) of patients with AR and of healthy individuals. In addition, we estimated the suppressive effect of CD4(+)CD25(+) Treg cells and allergen-specific, IL-10-secreting cells from both two groups. The frequency of CD4(+)CD25(+)Foxp3(+) T cells is similar in 43 AR patients compared with 38 healthy subjects. CD4(+)CD25(high) cells retain suppressive activity on allergen-stimulated cell proliferation and cytokine production of Th1 but not Th2 cells in both groups. However, the frequency of allergen-specific IL-10(+)IL-4(-)CD4(+) T cells is reduced in AR patients, and correlates inversely to clinical symptom scores. Allergen-specific, IL-10-secreting cells potently suppressed D. pteronyssinus major allergen 1-stimulated cell proliferation and cytokine production (IFN-gamma and IL-4) in healthy individuals. Altogether our data indicate that the number and function of CD4(+)CD25(+) Treg cells from allergic patients are not impaired. However, the deficiency of allergen-specific Tr1 cells may play a role in the development of AR.