Recombinant rat heterogeneous nuclear ribonucleoprotein H1 (hnRNP H1) reacted with 48% of sera from pSS patients and 5.2% of 153 sera from patients with other connective tissue diseases. Five of 11 pSS patients with no anti-SSA or -SSB antibodies had anti-hnRNP H1 antibodies. hnRNP H1 was suggested as novel, potential and additional diagnostic marker in pSS. The gene discussed is RO60; the disease is connective tissue disorder.