Prior studies have shown that patients with seropositive rheumatoid arthritis (RA) have an increased frequency of precipitating antibody against a nuclear antigen, the RA nuclear antigen, detected in human B lymphoblastoid cell lines infected by Epstein-Barr virus. The present investigations demonstrate that patients with seropositive RA also have specifically elevated titers of antibodies to another, better-characterized Epstein-Barr virus-associated B cell antigen, the Epstein-Barr nuclear antigen, which is detected by anti-complement immunofluorescence. Titers of these two antibodies were not affected by absorption of rheumatoid factor from serum. Furthermore, patients with RA did not have elevated titers of antibodies against the Epstein-Barr virus capsid antigen or to three other species of human herpesviruses: herpes simplex type 1, varicella-zoster virus, and cytomegalovirus. In both normal individuals and RA patients there was a significant association between the presence of antibodies to RA nuclear antigen and the titers of antibody to Epstein-Barr nuclear antigen. Thus, normal subjects with antibody to RA nuclear antigen had titers of antibody to Epstein-Barr nuclear antigen equivalent to those of patients with RA and significantly higher than normal subjects lacking antibody to RA nuclear antigen. One interpretation of these results is that patients with seropositive RA derive from a larger population with enhanced immune responsiveness to B lymphocyte nuclear antigens determined by the Epstein-Barr virus.