Systemic lupus erythematosus (SLE) is a clinically and serologically complex disease that demonstrates clinical, epidemiological and genetic differences among racial and ethnic groups. Some autoantibodies are useful for diagnosis of the illness. Others are clinically important because of associations with a particular manifestation of SLE. Antibodies to RNA helicase A (anti-RHA) comprise a newly described class of SLE autoantibodies. These antibodies have so far been found only in SLE patients and differ substantially in prevalence and nature between Mexican and white American SLE patients. Study of anti-RHA may provide insights into the origin of population differences in SLE.