The otic capsule of patients with otosclerosis contains premature bone with numerous cartilaginous remnants. Some investigators have proposed that the pathogenesis of otosclerosis is related to these cartilaginous rests in the otic capsule. In this study we investigated the presence of a humoral immune reaction against cartilage-specific antigens using ELISA-methods in patients with otosclerosis. Concomitantly, 8 age- and sex-matched healthy blood donors, free of any symptoms of autoimmune disease, served as controls. The following antigen substrates were used: collagen (I, II, III, VI, IX and XI), chondrocytes and chondrocyte membranes. Findings then showed that the levels of antibodies to collagens type II and IX as well as to chondrocytes were higher in the otosclerosis patients than in the control subjects. The high titer of antibodies against chondrocytes was not accompanied by an increase in antibodies against the chondrocyte membranes. To our knowledge these observations represent the first evidence for the existence of autoantibodies against minor collagens and chondrocyte-specific antigens and support a possible role for a cartilage-specific autoimmunity in the etiopathogenesis of otosclerosis.