To determine whether actual numbers of human herpesvirus 6 (HHV-6) genome in hematologic neoplasias are associated with disease condition, we developed a quantitative PCR-ELISA for detection of HHV-6. The amount of viral DNA was determined using externally amplified known amounts of the plasmid DNA containing the viral target sequences. First, we determined a viral burden in peripheral blood leukocytes obtained from 23 healthy volunteers and four specimens of lymph nodes with reactive hyperplasia. Using 1 microg of DNA, the prevalence of HHV-6 was 43.4% (10/23), ranging from 0 to 100 HHV-6 genomes in blood obtained from healthy volunteers. The amounts of HHV-6 genomes were < 10 in four non-neoplastic lymph node specimens. We next examined the amount of viral DNA in 21 blood specimens and 19 lymph node specimens obtained from patients with lymphoproliferative diseases (LPD) at the time of diagnosis. The number of HHV-6 genomes in most of the B-cell lymphoma was < 5 in both blood and lymph node specimens, however, two lymph node specimens obtained from immunoblastic lymphadenopathy (IBL) and T-cell lymphoma had very high levels of HHV-6 viral DNA (3705 and 810, respectively). We also found that HHV-6 genomes in peripheral blood were more than 1000 in two patients with chronic lymphocytic leukemia. For all LPD patients combined, there were significantly higher levels of viral DNA (200.6 +/- 654.8 HHV-6 genomes per 1 microg purified DNA) compared to those in healthy volunteers (10.0 +/- 21.0 HHV-6 genomes per 1 microg purified DNA) (P < 0.05). This study demonstrates that a high level of HHV-6 viral DNA is occasionally associated with LPD patients. Although it is still uncertain whether HHV-6 is related to the pathogenesis in LPD or not, our results suggest that measurement of HHV-6 genomes using PCR-ELISA may be useful not only to understand the mechanism of HHV-6 infection in hemopoietic neoplasia but also to manage the care of immnocompromised patients such as bone marrow transplant patients.