In a clinical and serological study performed on a large series of patients with different connective tissue diseases, anti-ribosomal ribonucleoprotein (rRNP) antibodies were detected only in a small proportion of sera with systemic lupus erythematosus (SLE). SLE patients positive for anti-rRNP autoantibodies showed a significantly higher incidence of hemolytic anemia. The reasons for this surprising association are still unclear; however, this finding suggests that rRNP precipitin might be considered as a useful marker of a particular subgroup of patients with SLE.