The disease specificity of antibodies to rheumatoid arthritis nuclear antigen (RANA) was examined by comparing anti-RANA titers in sera from 100 patients with rheumatoid arthritis (RA) with sera from 93 healthy controls. Anti-RANA antibodies were found in 86% of the RA sera and 56% of the controls. The higher titers in the RA sera were unrelated to clinical features or to measurements of circulating immune complexes or rheumatoid factors. To study the relationship of these antibodies to previous Epstein-Barr virus (EBV) infection, antibodies to the EB virus capsid antigen (VCA) were examined and found in 94% of the RA sera and 97% of the adult controls. Four of the six RA sera without anti-VCA antibodies had detectable anti-RANA antibodies, so that we might suggest anti-RANA can arise in the absence of EBV infection. From absorption experiments with non-EBV transformed extracts, we inferred that high anti-RANA titers could be due to reactions with non-Epstein-Bar virus related nuclear antigens. These data cast doubt on current speculation about a possible pathogenic role for Epstein-Barr virus in this disease.