Antibodies to collagen types I, II, and IV were measured in patients with otosclerosis and patients with Meniere's disease. Levels of antibodies to type II collagen were significantly higher in these patients than in control subjects, while no differences were found among levels of antibodies to collagen type I or type IV. These observations suggest a possible role for type II collagen autoimmunity in the etiology of otosclerosis and Meniere's disease.