Using Southern hybridization analysis, we have detected the Epstein-Barr virus (EBV) genome in 36 per cent (4/11) of enteropathy-associated T-cell lymphoma (EATL), a frequency much higher than that seen in nodal T-cell lymphomas in which we were able to show EBV DNA in only 3 per cent (1/30) of the cases examined. Using a terminal fragment probe, monoclonal proliferation of EBV in infected cells was demonstrated in three of the four EBV-positive EATL cases (in one case, insufficient signal prevented the determination of EBV clonality). The EBV genome and an early transcript, EBER1, were identified in tumour cells by in situ hybridization. Expression of latent membrane protein (LMP) was detected in two EBV DNA/RNA-positive EATL cases. In view of the known oncogenic properties of EBV and the putative central role of LMP in EBV-induced cell immortalization, the results of this study suggest that the virus may play an aetiological role in the pathogenesis of EATL.