The prevalence of anti-SSA (Ro) antibodies was investigated in 126 patients with various systemic rheumatic diseases and in 77 normal subjects. Also, we studied the relationship between these autoantibodies and the clinical features of our patients with SLE. Anti-SSA (Ro) occurred with a frequency of 14% in SLE but was not associated with specific clinical features of the disease. In Sjögren's syndrome the frequency was 25%, in rheumatoid arthritis 20.3% and in mixed connective tissue disease 15.4%. Finally, in the control group anti-SSA (Ro) antibodies were not present. We believe that the presence of this antibody is not specific to any rheumatic disease in our Mexican population, and should not be used as a "marker antibody" of some clinical features in patients with SLE.