Three hundred and forty-eight patients with well diagnosed CTD (101 SLE, 51 systemic sclerosis, 53 primary Sjogren's syndrome, 27 poly/dermatomyositis, 15 rheumatoid arthritis and 101 overlap CTD) and 31 matched healthy subjects were studied. In addition, sera from 13 patients with primary Epstein-Barr virus (EBV) infection (10 in acute primary infection and 3 with anamnestic past infection) and high titer IgG anti-EBV antibodies were tested. IgG anti-UsnRNP as well as anti-ribosomal P protein antibodies were determined by Western blotting on total Raji cell extract (a cell line transformed by EBV). Antinuclear and anti-dsDNA antibodies were detected by indirect immunofluorescence on HEp-2 cells and Crithidia luciliae respectively, anti-ENA by counterimmunoelectrophoresis. Statistical analysis was performed by chi-square test.