Spontaneous anti-DNA antibodies in autoimmune mice have the characteristics of antibody produced by Ag-specific, clonally selective B cell stimulation. The nature of the somatically derived antibody V region structures recurrent among spontaneous anti-DNA antibodies suggests that DNA or DNA-protein complexes may provide the antigenic stimulus for autoimmune anti-DNA antibody. In order to test this hypothesis directly, we have immunized normal, nonautoimmune-predisposed mice with complexes formed with DNA and an immunogenic, DNA-binding peptide. The highly immunogenic peptide, Fus1, forms an internal domain of a 128-amino acid ubiquitin-fusion protein from Trypanosoma cruzi. DNA-Fus1 complexes formed with native calf thymus DNA induced anti-DNA antibody in normal, nonautoimmune-predisposed mice that is similar in isotype and specificity to spontaneous anti-DNA antibody in (NZB x NZW)F1 autoimmune mice. The progressive nature of the development of dsDNA specificity in the immunized mice was also analogous to what is observed in the spontaneous anti-DNA antibody response of autoimmune (NZB X NZW)F1 mice. DNA-Fus1 immunized mice that produced IgG that bound to dsDNA had low to moderate levels of proteinuria and glomerular deposits of IgG. This experimental immunization system may be useful for understanding the immunologic basis for autoimmunity to DNA.