Anti-SS-A (Ro52/Ro60) autoantibodies have been described as serological marker for Sjögren's syndrome but are also found in patients with other systemic autoimmune diseases. Historically, these autoantibodies were considered as a uniform autoantibody-system. However, recent studies provided evidence that Ro60 and Ro52 are not part of a stable macromolecular complex and that anti-Ro52 and anti-Ro60 (SS-A) antibodies have different clinical associations. The prevalence of anti-Ro52 in systemic sclerosis and myositis is significantly higher than anti-Ro60 (SS-A) and isolated anti-Ro52 can be found in up to 37% of myositis patients, often correlated with anti-Jo-1 reactivity (p=0.0002). Furthermore, recent developments have made significant improvements in the quality of recombinant Ro60 showing excellent performance in Ro60 (SS-A) ELISA (Dr. Fooke Laboratorien). Of note, single reactivity to either Ro52 or Ro60 (SS-A) can be missed when measured with a classical SS-A ELISA based on a mixture of both antigens. Approximately 20% of anti-Ro52 or Ro60 (SS-A) positive samples may remain undetected using a mixture of both antigens. Moreover, the international reference sera from the Centers for Disease Control and Prevention (CDC 2, 3, 7, 10) were further characterized. It was concluded that Ro60 (SS-A) and Ro52 represent two distinct autoantibody systems and that separate detection is desirable in a clinical diagnostic setting.