Autoantibodies with specificity for enzymes involved in nuclear functions, including antibodies to RNA polymerase-1 and antibodies to enzymes involved in the synthesis of transfer RNA, have been identified in patients with rheumatic diseases. Autoantibodies reacting with amino-acyl-transfer RNA synthetases occur in the sera of 25% to 40% of patients with idiopathic inflammatory myopathies, polymyositis and dermatomyositis (82). An antibody named Jo-1 (anti-histidyl-transfer RNA synthetase antibody) was the first of these “antisynthetases”, which was discovered. Anti-Jo-1 has been reported in approximately 30% of patients with polymyositis and in 70% of patients with polymyositis who have interstitial lung disease. Since ELISA using recombinant fusion protein Jo-1 as antigen are more sensitive than double diffusion methods, ELISA should be used for the detection of anti-Jo-1 antibodies in patients with polymoyositis (83).