It is generally accepted that Hodgkin (H) and Reed-Sternberg (RS) cells are the neoplastic cells in the tissue of Hodgkin's disease. However, the etiology is still unknown. Epstein-Barr virus (EBV) genome was demonstrated in H/RS cells more than ten years ago and thereafter many studies supported the finding. It has been suggested that EBV plays an important role in pathogenesis of Hodgkin's disease. However, there are many cases of Hodgkin's disease which are EBV-negative. Thus, the search for an 'HD-associated' virus is necessary. Using microdissection, polymerase chain reaction, in-situ hybridization and immunohistochemical methods, we found not only cytomegalovirus genome but also its antigen is localized within H/RS cells. It suggests that, in addition to EBV, human cytomegalovirus might play a role in the pathogenesis of some EBV-negative cases of Hodgkin's disease.