An enzyme immunoassay was developed to detect antibodies to native DNA; DNA coating conditions that maximized sensitivity, specificity, and reproducibility were selected. Sera of patients with systemic lupus erythematosus (SLE) were positive more frequently by this immunoassay than by the Crithidiu luciliae assay or by counterimmunoelectrophoresis. By enzyme immunoassay, 94% of sera with active SLE and 70% of sera from patients with inactive SLE were positive, as were 16% from those suspected of having SLE, and 2.5% of normal persons. Specificity for native DNA was shown for both SLE and normal sera by inhibition studies and by S1 nuclease treatment of polystyrene-bound native DNA. The enzyme immunoassay correlated more with serum hemolytic complement levels than did the other 2 assays, suggesting that it detects biologically more relevant anti-DNA antibodies than do the other 2 tests.Measurement of serum anti-DNA antibody levels has been helpful in both the diagnosis and clinical assessment of systemic lupus erythematosus (SLE) detect antibodies to native DNA (nDNA), including immunodiffusion (7), complement fixation (8,9), agglutination (lO,ll), immunofluorescence (6,12), and radioimmunoassays (13-18). The sensitivity, specificity, cost, and ease of performance of these assays vary considerably (19,20).(The enzyme immunoassay (EIA) appears to offer advantages over other assays in areas of sensitivity, reproducibility, and efficiency, without sacrificing specificity. Since the initial description by Engvall and Perlmann (21), many antigens have been bound to solid phases to detect antibodies by EIA. Most of these antigens have been proteins or polysaccharides, but the binding of nucleic acids to polystyrene has not been systematically studied. Recently, several papers have appeared describing the application of EIAs to detect antibodies to DNA (22-29). In each of these reports different conditions were used, and the success of binding nDNA to the solid phase has varied (23,25).The purpose of the present study was to develop an EIA that could detect antibodies to nDNA, including a reproducible and reliable method for binding of DNA to the solid phase; this EIA was to be both sensitive and specific. In addition, the antibodies detected by the EIA were compared with those detected by other tests to define the (biologic) quality and relevance of the antibodies analyzed by different techniques. MATERIALS AND METHODSSource of sera. Normal human sera were obtained either from hospital personnel (sera kindly provided by Mr.