This retrospective study involved patients who received an allogeneic HSCT and were hospitalized at the Hematology, Oncology, and Internal Medicine Clinics, Medical University of Warsaw. In the period under consideration (December 2004 to October 2006) there were 38 patients receiving allogeneic stem cell transplants. The criteria for patient selection for the study included the appearance of at least one syndrome from those listed below within a period of 100 days after HSCT: pneumonia, appearance or intensification of graft-versus-host disease (GvHD), skin rash, or pyrexia of unknown origin. Introduction of these criteria resulted in a group to 26 adult receivers of HSCTs ( Table 1) . Monitoring of clinical status of the patients and viral load in blood samples comprised a period of 180 days after HSCT.