Antidouble stranded DNA (dsDNA) antibodies have been detected by a sensitive RIA in the sera of 28-100% of patients with Graves' disease, but it remains unclear whether these assays have detected authentic dsDNA antibodies. We have obtained sera from 42 patients with active Graves' disease and no known connective tissue disorders. All sera were tested for dsDNA antibodies by 2 quantitative RIAs (Farr assay and Millipore filter assay; normal, less than 20% for both assays) and by an enzyme-linked immunosorbant assay for antibodies to dsDNA and to single stranded DNA (ssDNA). All sera were negative for dsDNA antibodies by the Farr assay and by enzyme-linked immunosorbant assay, 2 of 42 had mildly elevated levels (33% and 23%) by the Millipore filter assay, and 7 of 42 were positive for ssDNA antibodies. The 2 positive sera for dsDNA antibodies were also tested using the Crithidia luciliae indirect immunofluorescence assay, and both were negative. Patients with Graves' disease have been reported to have an increased prevalence of antinuclear antibodies, but the more recent findings of dsDNA antibodies in these patients is of interest because dsDNA antibodies are considered to be specific for systemic lupus erythematosus. Our data suggest that true immunoglobulin G dsDNA antibodies are not elevated during active Graves' disease, and positive assay results may be due to measurement of ssDNA antibodies, immunoglobulin M dsDNA antibodies, or nonantibody DNA binding.