The autoimmune etiology suspected for some forms of hearing loss, supported by the clinical efficacy of steroid therapy, is thought to involve immune complexes, autoantibodies directed to the inner ear and/or cellular effectors. We report a study performed in 57 individuals with sudden deafness (n = 17, group 1) or progressive sensorineural hearing impairment (n = 40, group 2). A severe depletion in CD3+ and CD4+ peripheral lymphocytes was observed in group 1 and a marked decrease of CD8+ cells levels was observed in both groups. Group 2 patients frequently had anti-nuclear and anti-thyroid antibodies, while anti-cochlear antibodies were found in both groups (respective incidences, 75 and 71%). Anti-cartilage antibodies, found with a similar frequency in both groups, were not correlated with anti-cochlear antibodies. These data suggest that different immune disorders are involved in the development of sudden and progressive deafness, while both types of sensorineural hearing impairment involve immune abnormalities.