The thesis proved that different immunoassays could detect different rates of positivity in the same patient group; the Werfen CLIA could identify 8 positive samples that were negative in the Hycor ELISA, the Hycor anti-SSA IgA assay pointed at two additional patients having anti-SSA IgA antibodies. Anti-SSA IgA and IgG concentrations showed a significant correlation with disease activity, suggesting that the measurement of these autoantibodies could help the evaluation of disease activity in SS patients.