Epstein-Barr virus encoded RNA's (EBER) are small RNA species found in cells latently infected by the virus. The physiological function of these molecules is currently a matter of speculation. Nonetheless, their presence in extremely high copy number has made it possible to reliably detect the Epstein-Barr virus by in-situ hybridization, in human tissues routinely fixed with formalin and embedded in paraffin. Such studies have enhanced our understanding of a number of hematologic malignancies, particularly Hodgkin's disease, angiocentric immunoproliferative lesions and angio-immunoblastic lymphadenopathy. In addition, sequential EBER in-situ hybridization studies on lymphoid tissues should enable oncologists to monitor the development of lymphoproliferative disorders occurring in the setting of organ transplantation, AIDS and hereditary immunodeficiencies.