We have sequenced nine monoclonal antibodies (mAb) derived from C3H.SW mice in which experimental systemic lupus erythematosus (SLE) was induced. The hybridomas were selected for binding to DNA or to HeLa nuclear extract (NE). Three mAb were found to bind DNA, and are shown to exhibit sequence characteristics of pathogenic anti-DNA antibodies. One, mAb 2C4C2, is shown to use a heavy chain V region gene (VH) identical to the VH of anti-DNA mAb isolated from other lupus-prone mice, namely (NZB x NZW)F1. The light chain V region gene (VL) of mAb 2C4C2 is 98% homologous to the VL of another anti-DNA mAb, also isolated from (NZB x NZW)F1 mice. The other two anti-DNA mAb, 5G12-4 and 5G12-6, share 93% of their VH sequences with that of mAb 2C4C2. Six mAb bound proteins of HeLa NE. Four of these six antibodies were found to use the VH124 VH and V-L7 VL. The nine mAb use a total of five VH and four VL germ-line genes, demonstrating that the autoantibodies induced in mice with experimental SLE do not originate from one B cell clone. Three of these nine VH and VL were identical in sequence to germ-line genes, while at least three others had somatic mutations. The latter suggests that the above autoantibodies arise in mice by both usage of existing (pre-immune) B cells, and through an antigen-driven process. Furthermore, it appears that autoantibodies found in mice with experimental SLE use genetic elements similar to those used by mAb that were isolated from mouse strains which develop lupus spontaneously.