109 malignant lymphomas were surveyed by Southern blot analysis and polymerase chain reaction (PCR) for Epstein-Barr virus (EBV) DNA and compared with 16 examples of non-neoplastic lymphadenopathy and 4 normal thymuses. In specimens positive by the method of Southern and PCR, in situ hybridization studies were performed on formalin-fixed, paraffin-embedded sections. By Southern blot analysis, two of seven Hodgkin's disease samples (29%) (one of mixed cellularity and the other of lymphocyte predominance type), three of 56 B-cell lymphomas (5.6%) and five of 46 T-cell lymphomas (11%) demonstrated EBV DNA. However, the 16 examples of lymphadenitis and the 4 normal thymuses showed no EBV DNA. With PCR, EBV DNA was identified in one B-cell lymphoma, nine T-cell lymphomas, ten lymphadenitis specimens and two of the normal thymus, in addition to the positive specimens determined by the Southern blotting method. These results indicate that the presence of EBV DNA is not related to lymphoid malignancy, but enhancement of the DNA is demonstrated in some neoplastic conditions. By in situ hybridization, EBV genomes were not detected in all PCR-positive cases, but only in those positive by Southern blot analysis.