Epstein-Barr virus (EBV) is present in B cells in the blood of healthy people; few studies have looked for EBV in other cell types in blood from patients with lymphoproliferative disorders. We use a new technique combining immunofluorescent cell-surface staining and fluorescent in situ hybridization to quantify both EBV copy number per cell and cell types in blood from patients with high EBV DNA loads. In addition to CD20(+) B cells, EBV was present in plasmablast/plasma cells in the blood of 50% of patients, in monocytes or T cells in a small proportion of patients, and in "non-B, non-T, non-monocytes" in 69% of patients. The mean EBV copy number in B cells was significantly higher than in plasmablast/plasma cells. There was no correlation between EBV load and virus copy number per cell. Although we detected CD21, the EBV B-cell receptor, on EBV-infected B cells, we could not detect it on virus-infected T cells. These findings expand the range of cell types infected in the blood. Determining the number of EBV genomes per cell and the type of cells infected in patients with high EBV loads may provide additional prognostic information for the development of EBV lymphoproliferative diseases.