Epstein-Barr virus (EBV) is linked to a spectrum of human diseases including epithelial and lymphoid malignancies in which it exists predominantly in a latent state. EBV is capable of establishing replicative infection at oropharyngeal and genital sites. Replicative EBV infection also occurs in oral hairy leukoplakia, in EBV associated lymphoproliferative disorders, and to a minor degree in nasopharyngeal carcinomas. Recent evidence also suggests that EBV replication, also, may be associated with AIDS related lymphomas and Hodgkin's disease. However it is widely believed that virus in circulating B-lymphocytes and in B-cell malignancies is stringently latent. We now show that by Southern blot analysis we can detect replicative forms of virion DNA in 14.5% (8 of 55) of EBV-positive Burkitt's lymphoma biopsies. This may be the explanation for the elevation of the titres of lytic cycle EBV antigens that is associated with presentation and relapse of EBV associated Burkitt's lymphoma.