Agarose-poly-L-lysine (Ag-(lys)n-DNA) has been used to bind DNA for assay of anti-DNA antibodies (ab). In this work, an algorithmic approach has been used to classify antinuclear ab (ANA) as being directed against native DNA (dsDNA), denatured DNA (ssDNA), DNA-protein complexes (deoxyribonucleoprotein; DNP), and against antigens which are independent of DNA (iDNA). These ab were subjected to Ag-(lys)n-DNA, and the selectivity of this adsorbent for the various specificities of ab was determined. The DNA on the columns was left untreated or treated with S1 nuclease, this being effected either by treating the DNA prior to introducing it onto the columns or by adding S1 nuclease to the columns after the DNA was bound. Ag-(lys)n-DNA adsorbs ab directed against ssDNA and DNP as well as ab to dsDNA; iDNA ab are not adsorbed. S1 nuclease treatment does not effectively remove ssDNA regions from the Ag-(lys)n-DNA, but it does result in the abolition of the adsorption of a population of ab which are in the anti-DNP sera and contribute to the total ANA load. While anti-iDNA ab are not adsorbed onto the columns, they do contribute to the ANA titer, unlike anti-ssDNA ab which are adsorbed onto the Ag-(lys)n-DNA but do not contribute to the ANA titer. We conclude that Ag-(lys)n-DNA bears antigenic sites for dsDNA, ssDNA, and DNP ab and suggest that our understanding of the characteristic ab-binding profile of this versatile immunoadsorbent may have applications in the study of autoimmune diseases.