In this report, we investigated 73 cases of Hodgkin's disease (HD) and 752 consecutive cases of non-Hodgkin's lymphoma (NHL) to demonstrate EBV in the tumor cells by EBER in situ hybridization. For EBV positive cases, expression of EBNA1, EBNA2, LMP1 and P53 gene products were examined immunohistochemically, EBV-serology and prognostic data were also analyzed. EBV was detected in 48 (65.8%) of Hodgkin's disease in the tumor cells. EBV-positive HD showed expression of LMP1 and episomal monoclonality in all 5 cases examined. Among NHL, EBV was detected in 44 (12.0%) of 368 cases with ATL, 36 (31.6%) of 114 cases with T-ML, 18 (6.8%) of 263 cases with B-ML and none of 7 other types (p<0.00001). High prevalent expression of LMP1 (66%) and P53 gene products (80%) and low prevalent expression of EBNA1 and EBNA2 were observed in EBV-positive NHL cases with similar distribution of EBER ISH sporadic and diffuse positive cases. Episomal clonality of EBV were demonstrated in some cases examined. Elevated antibody titer particularly IgA antibodies against VCA and EA, and poor prognosis of EBV positive cases were observed.