Recurrent aphthous ulcerations (RAU) are a chronic inflammatory disease with evidence of inappropriate immune response. Previous studies have suggested cell-mediated activation of immune response towards common micro-organisms of oral cavity in RAU. In this investigation, we explored cytokine production by peripheral blood mononuclear cells (PBMC) and T regulatory cell population in blood of active and remission RAU patients as crucial factors for maintenance of peripheral tolerance. Ten patients with minor RAU and 12 healthy individuals were selected for the study. Cytokine levels were analysed in supernatants using Cytometric Bead Array Kit for flow cytometry and ELISA. We have demonstrated increased production of Type 1 cytokines IL-2, IFN-gamma and TNF-alpha as well as IL-5, IL-6 and IL-8 by peripheral blood mononuclear cells in RAU. In contrast, IL-10 and TGF-beta anti-inflammatory cytokine production was decreased in RAU patients compared to healthy individuals. Moreover, we have found that CD4(+)CD25(+high) T regulatory cell proportion was decreased in RAU and represented 3.58+/-0.654% of CD4(+) T cells in active RAU, 4.66+/-0.561% of CD4(+) T cells in remission RAU, whereas in healthy controls CD4(+)CD25(+high) T cells represented 7.30+/-1.238% of CD4(+) T cells (p<0.001). Thus, the obtained results indicate that disproportion in cytokine production may be contributing factor in the pathogenesis of RAU. Alteration in the number of CD4(+)CD25(+high) T regulatory cells in RAU may additionally influence the development of the disease. We propose that imbalance in pro- and anti-inflammatory cytokine network may lead to the breakdown of peripheral tolerance in RAU and the excessive immune response towards harmless micro-organisms colonized oral mucosa or self-antigens.