Though at present there is no evidence-based algorithm for the treatment of primary Sjögren's syndrome, it is generally accepted that glucocorticosteroid (GS) therapy must be introduced in cases with severe systemic manifestations. As the side-effects of the GSs are well known, it would be useful to know in advance how the patients will respond to this type of treatment. For this reason we measured the in vitro steroid sensitivity of 29 SS patients using inhibition of antibody dependent cellular cytotoxicity (ADCC) test by methylprednisolone compared to that of 28 controls. SS patients proved to be significantly less sensitive to GSs than controls (inhibition of ADCC reaction: 42.4 vs 53.1%; p < 0.01). This was especially true in SS patients with anti-SSA and/or SSB autoantibody positivity and with HLA-DR2 and/or -DR3 alleles. Comparing the results of the in vitro GS sensitivity and the clinical effectiveness of the previously applied corticosteroid therapy it seems that steroid inhibition of ADCC reaction has a predictive value in determination of in vivo sensitivity to GSs. However, in patients with decreased in vitro GS sensitivity a more expressed in vivo steroid sensitivity cannot be excluded.