We did not find any correlation between viremia and the applied conditioning regimen or anti-GvHD prophylaxis. All of the HHV-6-positive graft recipients had fever of unknown etiology during the six weeks after SCT and half of them (4 persons) had acute GvHD features. Sixty-three percent of the described patients had pneumonia and 38% skin rash. No Epstein-Barr virus or CMV DNA was found in all the plasma samples during HHV-6 onset ( Table 1) .