AbstractInfections with the β‐herpesviruses human herpesvirus‐6 (HHV‐6) and human herpesvirus‐7 (HHV‐7) are ubiquitous in childhood. The immunosuppression secondary to organ or bone marrow transplantation together with posttransplantation management may favour viral replication and reactivation. HHV‐6 and ‐7 induce immunosuppression by targeting lymphocytes, natural killer cells and monocytes. HHV‐6 is commonly detected posttransplantation but variability in definitions of clinical syndromes related to this virus and detection methods have complicated understanding of the clinical relevance of HHV‐6 posttransplantation. Clinical symptoms associated with HHV‐6 include febrile illness, pneumonitis, hepatitis, encephalitis and bone marrow suppression. However, the majority of HHV‐6 infections are asymptomatic. The incidence of HHV‐7 infection and its clinical manifestations posttransplantation are even less well characterised. In addition, HHV‐6 and HHV‐7 are related to CMV disease or acute graft‐versus‐host disease and, indirectly, to increases in resource utilisation. Based on the potential relevance of these two β‐herpesviruses in transplant recipients, further studies are required to establish their real impact in transplantation. For this, sensitive and specific molecular diagnostic techniques allowing for the rapid detection and quantitation of virus and for the analysis of susceptibility to current antiviral agents are required. Copyright © 2001 John Wiley & Sons, Ltd.