Epstein-Barr virus (EBV) has been proposed as a possible infective agent involved in the pathogenesis of angioimmunoblastic lymphadenopathy (AIL), a progressive and often fatal lymphoproliferative disorder. We have studied 19 cases of AIL-like lymphomas for the presence of EBV using a sensitive in situ hybridization technique based on the detection of Epstein-Barr encoded RNAs with digoxigenin-labelled oligonucleotide probes. EBV was found in 11 cases; in seven of these EBV was detected in occasional cells. Immunocytochemical studies to investigate viral gene expression, revealed the presence of EBV-encoded latent membrane protein only in those cases which had appreciable numbers of positive cells by in situ hybridization. The intensity of staining varied from case to case and the overall proportion of cells staining for latent membrane protein in a given case was considerably less than that by in situ hybridization. In situ hybridization for cytomegalovirus and human herpes virus type-6 was negative in all cases. We discuss these findings in the light of the proposed role of EBV in the pathogenesis of AIL and conclude that the presence of EBV is a consequence of the disease rather than the cause.