The presence of Epstein–Barr virus (EBV) DNA in biopsy tissues from patients with Hodgkin's disease (HD) was investigated by the polymerase chain reaction (PCR) using primers specific to a sequence within the EBV Bam H1W region. EBV genome was detected in 33 of 57 (58 per cent) cases of HD. Viral DNA was, however, also demonstrated in nine of 24 non-Hodgkin's lymphomas, in three of nine non-neoplastic lymph nodes and in seven of 12 normal peripheral blood samples used as controls. In all cases, the band obtained following PCR was verified using Southern blotting and hybridization with highly specific Bam H1W probes. The results suggest that the technique is sufficiently sensitive to detect EBV in persistent latent infection in B-lymphocytes. Distinction between virus present as a possible aetiological agent of malignancy or as a latent infection is not possible when PCR is used under these conditions. The possible role of EBV as an aetiological agent of HD remains unresolved.