Sera were tested from 23 patients with systemic lupus erythematosus followed over a period of 1 to 5 years. Antibodies to native DNA were measured and correlated retrospectively with clinical evidence of disease activity. The overall degree of correlation between the presence of DNA antibodies and evidence of disease activity was good (P less than 0-001). Of 206 sera tested, only 4 had a normal DNA antibody at a time when significant clinical activity was noted. In contrast, 34 sera had mild to moderately raised DNA antibody levels at times of clinical remission. Although DNA antibodies are a useful investigation in the monitoring of disease activity, changes in therapy should not necessarily be made on DNA antibody levels alone.