Sera from patients with connective tissue diseases were tested for antibody against the Epstein-Barr virus (EBV) by indirect immunofluorescence and immunodiffusion. There were no significant differences between patient groups and controls in percent seropositive or titer by immunofluorescence. With immunodiffusion against EBV antigens, sera from patients with systemic lupus erythematosus (SLE) had a greater mean number of bands than controls and a miscellaneous group, though not the other patient groups. Many bands apparently unrelated to EBV were detected. A new pattern of nuclear fluorescence was seen which, when present, appeared in 75% to 85% of cells. This consisted of crossing strands of fluorescence confined to the nucleus, in contrast to the homogenous cellular fluorescence seen with EBV-specific reactions. Recognizing antibody activity not specific to EBV infection will be useful to workers employing these tests in future seroepidemiologic studies.