The risk to develop lymphoma is doubled in patients with rheumatoid arthritis (RA) in the absence of immunosuppressive therapy. This risk is slightly increased by the use of methotrexate or tumour necrosis factor alpha inhibitors (infliximab and etanercept) . Epstein–Barr virus (EBV) is detected in about one-third of lymphoma developing in RA patients. The reason why some patients develop lymphoma is unknown. We have previously shown that RA patients have an almost 10-fold increase of EBV load in their peripheral blood mononuclear cells (PBMCs), compared with normal controls . RA patients' peripheral blood EBV load is similar to that of healthy transplant recipients (10 copies per 500 ng DNA). In immunosuppressed transplant recipients, elevation of PBMC EBV load above 500 copies/500 ng DNA predicts the emergence of lymphoma.