In a cross-sectional study of 100 healthy elderly individuals, anticardiolipin antibodies (aCL) were measured using an ELISA technique. aCL were not detected in the majority of subjects (63%), and in the remaining 37% titres were within the laboratory reference range (mean +5 standard deviations) previously determined for adults of all ages. In contrast, significant titres of IgM rheumatoid factor were found in 10%, antimitochondrial antibody in 13%, antinuclear factor in 5%, anti-smooth muscle antibody in 18%, antiparietal cell antibody in 10%, and antireticulin antibody in 1%. Antibodies to single or double-stranded DNA were not detected in any subject. We conclude that, although other auto-antibodies may be present in the healthy aging population in Britain, abnormally elevated levels of aCL antibody do not occur, and when present may be an indicator of autoimmune-mediated pathology.