Regarding the amplification results of DNA isolated from plasma using HHV-6-specific PCR, expressed as the presence of exponential increases in fluorescence, products were detected in 29 samples (10%) taken from 10 patients (38%). Two of them (8%) had HHV-6 DNA in only a single positive sample and another 8 (30%) had positive results in two or more subsequent tests. In the patients with two or more plasma samples containing HHV-6 DNA, viremia was observed between days 18 and 40 after transplantation (Table 1 ). In the two patients who had a single HHV-6-positive blood sample, viral DNA was detected at a later time. The quantitative results obtained by the MutaREAL ® HHV-6 test in all positive cases were at low levels, between 700-1600 copies/ml. HHV-5 DNA was detected in the plasma samples collected from four HHV-6-negative patients. In all four cases, HHV-5 DNAemia was observed in the typical period of 40-65 days after transplantation and, moreover, a second HHV-5 viremia course occurred in two patients starting at days 103 and 123 after transplanta- Abbreviations: ALL -acute lymphoblastic leukemia, AML -acute myeloid leukemia, CML -chronic myeloid leukemia, MDSmyelodysplastic syndrome, rPBSCT -related peripheral blood stem cell transplantation, uPBSCT -unrelated peripheral blood stem cell transplantation, uCBSCT -unrelated cord blood stem cell transplantation, rBMT -related bone marrow transplantation, uBMT -unrelated bone marrow transplantation, -: negative, +: positive in one plasma/serum sample, ++: positive in two or more plasma samples. Abbreviations: ARDS -acute respiratory distress syndrome, CNS -central nervous system, GvHD -graft-versus-host disease, N/A -not applicable, -: negative, +: positive in one plasma/serum sample, ++: positive in two or more plasma samples.