The immunoreactivity of sera from patients with rapidly progressive sensorineural hearing loss (SNHL) or Menière's disease with bovine inner ear material was determined using the Western blot technique. Patients with other otologic conditions, autoimmune disorders, or arthritic disorders and age-matched randomly chosen patients with no hearing complaints served as controls. Twenty-two percent of the patients with bilateral rapidly progressive SNHL and 30% of the patients with Menière's disease had antibodies that reacted with a 68 kd antigen in the inner ear material. In the control groups, the incidence of reactivity was 5.0% (P < .001). When the results of this study were compiled with data collected previously, it was found that of 279 patients with bilateral rapidly progressive SNHL, 90 (32%) were positive with the 68 kd protein. Thus, the anti-68 kd antibody may provide a good marker for an immune etiology of these patients' hearing loss.