Aids in the diagnosis of Sjögren’s syndrome (especially with vasculitis) and lupus patients with Sjögren’s overlap syndrome. SS-A(Ro) is found in 60% to 70% of patients with Sjögren’s syndrome and 30% to 40% of patients with SLE. SS-B(La) is found in 50% to 60% of Sjögren’s syndrome and 10% to 15% of SLE. SS-A and SS-B are particularly useful in “ANA-negative” cases of SLE, being present in a majority of such cases. Patients who are ANA-positive and who have SS-A but not SS-B are very likely to have nephritis. Antibodies to SS-A are also associated with HLA loci DR3 and DR2 and with hereditary deficiency of C2. Patients with SS-A may also have antibodies to cardiolipin, lupus anticoagulant, and clinical thromboses.