Another virus belonging to the β-herpesvirinae subfamily, HHV-5 (CMV), is one from the most important viral pathogens causing clinical infections in patients receiving immunosuppressive treatment. As there is information in published data about a connection between HHV-5 and HHV-6 reactivation in graft recipients, our aim was to determine the appearance of simultaneous reactivation of both β-herpesviruses. We believe that this is probably the first report from Poland involving this kind of examination in HSCT recipients.