Epstein-Barr virus (EBV) has been associated with Hodgkin's disease (HD) in up to 50% of cases, but the subtype of EBV involved has only recently been studied. In this report, biopsy samples from 30 patients with HD were assessed for EBV sequences using both the polymerase chain reaction (PCR) and in situ hybridization (ISH). EBV sequences were localized to the malignant Reed-Sternberg cells and their mononuclear variants (Hodgkin's cells) in 9 of the 30 cases, with 7 demonstrating A-type and 2 B-type EBV sequences. Both of the patients with B-type EBV-associated HD had features to suggest pre-existing immune compromise: one was infected with human immunodeficiency virus (HIV) and had severe CD4+ T-lymphocyte depletion; the other was a debilitated elderly patient with dementia. A previous study suggested that A-type EBV alone is associated with HD and the finding of predominantly A-type EBV in the present series is in keeping with this report. The presence of B-type EBV in the HD of patients with pre-existing immunodeficiency, taken together with the recent report that B-type EBV occurs in HIV-associated non-Hodgkin's lymphoma, suggests that B-type EBV may be an important human pathogen in immunocompromised patients.