Attention has been directed lately to antibodies reactive with double-stranded DNA (dsDNA) in systemic lupus erythematosus (SLE) patients, as these antibodies are of considerable diagnostic value and are thought to be involved in the pathogenesis of the disease. In the present study, the clinical and laboratory evaluations of 30 SLE patients in various stages of disease activity were correlated with the levels of anti-DNA antibodies, as detected by the methods of Farr and of Aarden et al. Sera of 65 patients in relapse or remission were examined with both techniques, and a discrepancy was found in only nine sera. In addition, in six patients, a differential analysis of the immunoglobulin classes of anti-dsDNA was performed according to the method of Aarden et al. The data obtained with this assay correlate well with SLE activity and thus may add an important step to the evaluation of SLE patients.