Specific subtypes of malignant lymphoma are highly associated with Epstein-Barr virus (EBV) infection. In the present study, the authors evaluated EBV-encoded RNA (EBER) expression by in situ hybridization in 300 cases of malignant lymphomas diagnosed by lymph node biopsy, with 100 cases of reactive lymphoid hyperplasia in lymph nodes as controls, for comparison. There were 100 consecutive cases of classical Hodgkin’s lymphoma (cHL), 100 consecutive cases of non-Hodgkin’s lymphoma, B cell (NHL-B), and 100 consecutive cases of non-Hodgkin’s lymphoma, T cell (NHL-T). EBER expression was detected in 46% of reactive lymphoid hyperplasia cases, but the positively stained cells in those cases constituted less than 5 percent of the total cell populations. When using the presence of EBER in 5 percent or more of the cell population and/or the presence of EBER in the Hodgkin’s Reed- Sternberg’s cells as indicators of positivity, 64% of cHL, 13% of NHL-B, and 51% of NHL-T were found to be positive. The study indicates a strong association of cHL and NHL-T with EBV infection, the link apparently being weaker for NHL-B except for the subtypes of Burkitt’s lymphoma and diffuse large B cell lymphoma.