Antibodies to DNA (anti-DNA) occur prominently in systemic lupus erythematosus and provoke inflammatory damage in the kidneys. To determine the factors that confer pathogenicity on antibodies of this specificity, we investigated the in vitro and in vivo glomerular binding by members of four clonally related sets of monoclonal anti-DNA antibodies from lupus mice. Somatic mutations within the clonal sets enhanced binding to double-stranded DNA (dsDNA). Binding to permeabilized glomeruli in vitro was observed among affinity-purified preparations of these antibodies independent of specificity for dsDNA. In normal mice injected with hybridoma cell lines, nephritis as assessed by histology and immunofluorescence did not correlate with antibody affinity for DNA. By multivariate analysis, in vitro glomerular binding was the most predictive parameter of histologic outcome. These findings indicate that somatic mutations occurring during maturation of the autoimmune response do not necessarily enhance pathogenicity.