Background 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 betal (TGF-beta 1) in the cause of OME in adults, and to investigate the probable role of Foxp3(+)CD4(+)CD25(+) T cells in OME. Methods The concentrations of IL-10 and TGF-beta 1 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-beta 1 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. Results (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), so was TGF-beta 1 (both P<0.01). The concentration of IL-10 in MEEs was significantly higher than that in plasmas, not only in acute OME (P<0.01), but also in chronic OME (P<0.01). In chronic OME, the concentration of TGF-beta 1 in MEEs had no statistical difference with those in plasmas of the same patients. However, the concentration of TGF-beta 1 in plasmas of patients with chronic OME was significantly higher than that in plasmas of normal volunteers (P<0.01). (2) The concentrations of IL-10 and TGF-beta 1 in MEEs of the patients who had been treated more than once were higher than those MEEs of the patients who were treated for the first time, respectively (P<0.05, P<0.01). The level of TGF-beta 1 in plasmas of the patients who had been treated more than once was higher than in those of the patients who were treated firstly (P<0.05), while the level of IL-10 in plasmas had no difference. The concentration of IL-10 in mucoid MEEs was higher than those in serous ones (P<0.05), while TGF-beta 1 had no statistical difference between mucoid and serous MEEs (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-beta 1 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). Conclusions IL-10 and TGF-beta 1, 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. Chin Med J 2009; 122(18).2149-2154