Otitis media with effusion (OME) is a disease with complicated pathogeneses which are not clearly known. Increasing interest has been focused on immunological cells, cytokines and their roles in chronic inflammatory states. This study was designed to disclose the existence and roles of interleukin-10 (IL-10) and transforming growth factor beta1 (TGF-beta1) in the cause of OME in adults, and to investigate the probable role of Foxp3(+)CD4(+)CD25(+) T cells in OME.The concentrations of IL-10 and TGF-beta1 in the middle ear effusions (MEEs) and plasmas of 36 adults (45 ears) with OME were measured by means of enzyme linked immunosorbent assay (ELISA). As contrast, the concentrations of IL-10 and TGF-beta1 in the plasma of 30 normal volunteers were measured using the same method. Furthermore, the proportion of Foxp3(+)CD4(+)CD25(+) T cells in CD4(+) T cells of blood was tested by flow cytometry.(1) The concentrations of IL-10 in all MEEs and plasmas of the chronic OME patients were higher than those in patients with acute OME (both P 0.05). The concentration of IL-10 in MEEs had a strong correlation with the duration of the illness (r = 0.547, P < 0.01). The same correlation was also found between the concentration of TGF-beta1 in MEEs and the times patients being treated (r = 0.579, P < 0.01). (3) The proportion of Foxp3(+)CD4(+)CD25(+)T/CD4(+) T cells in the blood of chronic OME was not only significantly higher than that in the acute OME (P < 0.01), but also higher than that in normal volunteers (P < 0.01). In chronic OME, there was a correlation between the proportion of Foxp3(+)CD4(+)CD25(+) T/CD4(+) T cells in the blood and the concentration of IL-10 in the plasmas (r = 0.602, P < 0.05).IL-10 and TGF-beta1, as two important immunoregulatory mediators, participate in middle ear inflammatory response, especially in chronic course of OME in adults. Foxp3(+)CD4(+)CD25(+) T cells may play some immunoregulatory roles in the course of this disease.