Fifty-six sample pairs of middle ear effusions and sera obtained from patients with otitis media with effusion were investigated for The IgE antibody activity against mites, using radioallergosorbent test (RAST) which was recently developed as an in vitro allergy test. The IgE concentrations were also determined by radioimmunosorbent test (RIST). Results showed that the IgE antibody activity against this allergen was found in 5 middle ear effusions and 3 sera. Four of 5 patients with the positive RAST test had nasal allergy or signs suggesting allergy. Theree were two middle ear effusions which seemed to be an allergic fluid. However, findings in the present study do not suggest that middle ear effusions result from the direct allergic reaction induced by mites in the mucous membrane lining the middle ear cavity.