Autoantibodies to human carbonic anhydrase II (CAII) were screened by ELISA in 109 sera from Asian Japanese patients with systemic lupus erythematosus (SLE), primary Sjögren's syndrome (Sjs), progressive systemic sclerosis (PSS) and dermatomyositis (DM). Anti-CAII antibodies were positive in 24.1% of SLE, 20.0% of primary Sjs, 16.7% of PSS and 25.0% of DM. On the other hand, sera from atopic dermatitis, bullous pemphigoid and psoriasis patients showed no activity for anti-CAII antibodies. CAII could be a common exonuclear autoantigen in subsets of rheumatic autoimmune diseases.