Epstein-Barr virus (EBV) is a human lymphotrophic herpesvirus implicated in the development of several lymphoid malignancies. Recently, detection of cell-free EBV DNA in sera or plasma from patients with EBV-associated malignancies has been reported. However, most published studies are qualitative in nature, with only a few providing quantitative data. We have described the temporal changes of plasma EBV DNA levels in patients with EBV-associated lymphoid malignancies during therapy using quantitative real-time PCR. A close correlation between plasma EBV DNA levels and therapeutic response was observed. Our aim was to update our results and to assess the role of the plasma EBV DNA levels as a molecular marker for disease monitoring in patients with EBV-associated lymphoid malignancies.