Previous studies showed a link between systemic lupus erythematosus (SLE) and Epstein-Barr virus (EBV) infection. We sought to determine the features of serologic response to EBV in SLE patients and whether this response differs from those of systemic sclerosis (SSc) and primary antiphospholipid syndrome (PAPS) patients as well as healthy individuals. Sera from 198 consecutive SLE patients have been tested to detect IgG antibodies to EA/D, EBNA-1, VCA P18 and for comparison, cytomegalovirus (CMV) using commercially available ELISA kits (Trinity Biotech, USA). Forty-six SSc patients and 38 PAPS patients were enrolled as diseased control groups and sixty-five individuals as healthy controls. Significantly more SLE (54%, P = 0.001, OR 5.77, 95% CI 2.8-11.6), SSc (41.3%, P = 0.005, OR 3.4, 95% CI 1.4-8.2) and PAPS sera (36.8%, P = 0.023, OR 2.86, 95% CI 1.14-7.22) reacted against EA/D than healthy controls (16.9%). The mean age of anti-EA/D-positive SLE patients was significantly higher, and their disease duration was longer compared to anti-EA/D-negative SLE patients (41 +/- 14 vs. 33.8 +/- 10.8 years, P < 0.001 and 100 +/- 73 vs. 71 +/- 62 months, P = 0.003). In SLE patients, EA/D reactivity was associated with Raynaud's phenomenon and the presence of any anti-ENA antibodies. Although it did not reach a statistical significance, anti-EBNA-1 reactivity was slightly lower in patients with SLE. The frequency of anti-CMV Ig G positivity was found significantly higher in SLE patients (100%) when compared to patients with SSc (95.7%), PAPS (94.7%) and healthy controls (95.4%) (P = 0.035, P = 0.025 and P = 0.015 respectively). Our results support the proposed link between EBV and SLE. The finding that SSc and PAPS patients also have increased frequency of anti-EA/D response has revealed that this immune interaction may not be unique to patients with SLE, and there may be a common mechanism involving EBV in these autoimmune diseases.