It has been suggested that the activated local immune system is present in the middle ear and the effusion may be due to a local immune reacion in the middle ear. Several components of the immune response have been identified in effusions from patients with otitis media with effusion(OME). Interleukin 6(IL-6) is a cytokine with pleiotropic activities such as terminal differentiation in B cell, activation of T cells and support of multipotential colony formation by hematopoietic stem cells. We measured the levels of IL-6 in middle ear effusions using immune radiometric assay that is more sensitive and specific than enzyme linked immunosorbent assay or radioimmunoassay. The levels of IL-6 in mucoid effusions were significantly higher than those in serous effusions(p<0.05). IL-6 was observed at the lowest levels in effusions of patients over than 11 year of age(p<0.01). The results suggest that IL-6 may play a important role as inflammatory mediator in the chronically persistent stage of OME in children.