Otitis media with effusion is a common disorder in children and occurs more frequently in adults than has been generally appreciated. Laboratory tools have permitted a more specific characterization of this disorder by objective means. These laboratory tests include specific ear tests (pneumatic otoscopy, pure tone, and impedance audiometry), nasal tests (inflammatory cytology), functional tests for obstruction (airway resistance measurements), and anatomic tests of obstruction and inflammation (radiographic of nose and paranasal sinuses). Immunologic tests define the presence of hypersensitivity (skin testing, RAST) and immunodeficiency in this disorder.