A 77 year-old woman was admitted to the hospital because of nasal obstraction on March 1994. Tumorectomy of the nasopharyngeal tumor disclosed non-Hodgkin's lymphoma (LSG : diffuse, medium sized). The patient was treated with local radiotherapy to nasopharyngeal region and combined chemotherapy (2 courses of CHOP) to reduce residual tumor. On July, the pericardial effusion appeared and the large granular lymphocyte (LGL) like lymphoma cells were observed in the effusion. Flow cytometic analysis of these cells showed that they expressed CD 2, CD 7, CD 56 and HLA-DR, but did not express CD 3. T-cell receptor gene (TCR beta) rearrangement was not observed and natural killer activity was detected in these lymphoma cells. The patient was treated with ProMACE and the pericardial infusion of methotrexate, carboplatin and prednisolone, but the patient died of heart failure. Monoclonarity of lymphoma cells in the pericardial effusion was determined by southernblot analysis, using the terminal repeat of Epstein-Barr virus (EBV) for probe. It was suggested that EBV participated in tumorgenesis in this case.