Serum from patients with systemic lupus erythematosus (SLE) and hybridoma culture fluids derived from the fusion of SLE lymphocytes contain antibodies to native DNA (nDNA) and denatured DNA (dDNA). A rapid, efficient solid phase radioimmunoassay (RIA) was developed to screen for minute quantities of these autoantibodies. The RIA, which utilized polystyrene tubes, required the addition of 0.1% bovine serum albumin and 0.01% Tween 20 detergent to decrease nonspecific immunoglobulin binding. Pretreatment of the polystyrene tubes with poly-L-lysine (PLL) prior to coating with DNA increased the binding of radiolabeled nDNA from 15 to 46% and of dDNA from 17 to 63%. This PLL precoating step resulted in a 3-fold increase in the specificity of the assay for nDNA but was not advantageous for dDNA. The method described is sensitive, specific, and can be applied to the screening of microgram quantities of anti-DNA autoantibodies in serum and hybridoma culture fluids.