The Epstein-Barr virus (EBV) is a transforming herpes virus which is found in high frequencies in lymphoproliferative disorders arising in immunocompromised patients. To address the question of viral involvement in lymphomas of immunocompetent patients, we investigated 299 nodal and extranodal non-Hodgkin's, non-Burkitt's lymphomas of B- and T-cell lineage for the presence of EBV DNA. Epstein-Barr nucleic acid sequences were detected in 23 of 226 (10%) cases of B-cell lymphomas, in 24/72 (33%) T-cell lymphomas and one non-B, non-T lymphoma. Our data imply a possible role for the EBV in lymphoma development or propagation, an influence of viral factors on morphology and an impact of the anatomic site in which lymphoma development occurs.