Using Crithidia luciliae fluorescent assay a significant prevalence (7.6%; P less than 0.006) of anti-double-stranded DNA antibodies was found in a healthy old population. A negative enzyme-linked immunosorbent assay for anti-total histone antibodies excluded a false-positive reaction. Anti-double-stranded DNA antibodies in the aged differed from those found in patients with systemic lupus erythematosus and were characterized by a low titer (95.6% of cases), belonging to the IgA class alone (95.6%), no complement-fixing ability (100%), and negativity to Farr assay (100%). It is concluded that, in elderly subjects without signs and symptoms of disease, including systemic lupus erythematosus, such a peculiar anti-double-stranded DNA antibody may be detected.