Sera from 3528 patients with autoimmune disease, and non-autoimmune disease, and 500 normal individuals were studied for the presence of anticentromere antibodies (ACA) by indirect immunofluorescence on HEP-2 cells. Sixty-seven specimens were identified showing discrete speckled staining: 55 (82.1%), 11 (16.4%), and one (1.5%), were from patients with autoimmune disease, non-autoimmune disease and normal control subjects, respectively. These ACA were present frequently in CREST syndrome (55%), Raynaud's disease (29.6%) and primary biliary cirrhosis (30%). Only 16.4% of the antibody positive patients carried a clinical diagnosis of CREST, which means that ACA are not specific for CREST syndrome. High antibody titre persisted irrespective of whether or not the patients had active disease. The ACA were present infrequently in Sjögren's syndrome, systemic lupus erythematosus, rheumatoid arthritis, immune thrombocytopenic purpura, Graves' disease, immune haemolytic anaemia, and vitiligo. Sera from 107 patients with various other autoimmune diseases were negative for ACA.