Immunization of NZB and A/J mice against an anti-DNA hybridoma antibody (F227) derived from (NZB x NZW)F1 (B/W) mice allowed the preparation of two anti-idiotypic antisera. These two reagents were shown to recognize different idiotopes of the F227 monoclonal antibody. NZB anti-idiotypic antibodies recognized non-ligand-modifiable idiotypic determinants. These idiotopes were private or present at undetectable level in BW mouse sera since it was found that only two of the 24 B/W mouse sera tested were recognized by these antibodies. Conversely, A/J anti-idiotypic antibodies recognized partially ligand-modifiable idiotopes which were found in all B/W mouse sera tested. These results demonstrate that anti-DNA antibodies share similar idiotypic specificities and suggest that these autoantibodies occur as families of structurally related proteins.