The specificity of a panel of murine monoclonal anti-DNA antibodies for DNA antigenic determinants was evaluated by testing their relative binding to various animal and bacterial DNAs. The antibody panel consisted of six monoclonal anti-DNAs of MRL-lpr/lpr and B6-lpr/lpr origin, while the antigens tested were calf thymus (CT), salmon testes (ST), E. coli (EC) and Micrococcus (MC) DNA. While all antibodies bound to CT, ST, and EC DNA to a similar extent by direct ELISA, only one showed an equivalent level of interaction with MC DNA. The relationship of antigenic sites recognized by the antibodies was evaluated further by competition ELISA, assessing the ability of the anti-DNAs to block the interaction of a biotinylated anti-DNA with solid-phase DNA antigen. For each of the DNAs tested, two patterns of DNA interaction could be distinguished on the basis of the relative inhibitory activity of the different monoclonals. These results suggest that anti-DNA antibodies can be characterized using naturally occurring DNAs, with the observed patterns of binding suggesting recognition of unique antigenic sites, some of which are discrete and non-overlapping.