The prevalence of serum anti-DNA antibodies was evaluated by ELISA using oxidatively damaged DNA as antigen in 21 patients with systemic lupus erythematosus (SLE), in 9 spouses and in 15 first-degree relatives. These were compared with 12 healthy controls. There was no significant difference in the levels of serum antibodies detected between the group of spouses and normal controls with all results within the normal range of the assay. Binding of serum antibodies to the oxidatively damaged DNA was detectable in 12 (80%) of the relatives studied, and the range of values obtained overlapped significantly with the SLE patient group. The relevance of these antibodies to the immunopathology of SLE is unclear since they appear to be present in the absence of any clinical symptoms. However, they may be useful predictively as a marker for those individuals who are more likely to develop SLE.