Receptor editing or secondary Ig gene rearrangement occurs in immature, autoreactive B cells to maintain self-tolerance. Here we show that nonspontaneously autoimmune mice immunized with a peptide mimetope of DNA develop peptide- and DNA-reactive antibodies. Antigen-specific B cells display a follicular B cell phenotype. As these cells move into the memory compartment, many express RAG protein and acquire expression of both κ and λ light chains. Thus, this study provides evidence for receptor editing occurring in a mature, antigen-activated B cell population. Because the receptor editing observed here occurred in an autoreactive response to antigen, it may function to maintain peripheral tolerance.