Human cytomegalovirus is a ß human herpesvirus characterized by its restricted host range, production of nuclear as cytoplasmic inclusions, and its long life cycle. It is the largest known human herpesvirus, with genome of about 240 kb. CMV establishes latency in peripheral blood monocytes and tissue macrophages and can reactivate during HSCT. CMV is one of the most common viruses after HSCT and had been the most common infection cause of death. During the two decade ago, major advances have been achieved regarding the management CMV infection and disease. These advances have been made possible through the development of new diagnostic techniques for the detection of the virus and through the performance of prospective clinical trials of antiviral agents. Two principal strategies have been used for prevention of CMV disease: prop-hylactic strategy in which regular administration of an antiviral is used to prevent CMV reactivation and preemptive strategy in which reactivation of CMV is screened for during the period of higher risk and antiviral therapy promptly initiated when CMV reactivation occurs. In 1993 was realized the first HSCT in Bone Marrow Transplant Unit, State University of Campinas (Brazil), using the prophylactic strategy with intravenous ganciclovir in allogenic HSCT recipient but without using assays for monitoring active CMV infection in post-transplant. Surveillance of active CMV infection began in 1996 by PCR and serology. Preliminary results of this protocol were exhibited in the 2nd meeting of the European Haematology Association - Paris , France (1996). Preemptive strategy was deployed in 2004 by Bonon et al. In this research was described the Bone Marrow Transplant Unit, State University of Campinas (Brazil) experience in the control of active CMV infection following HSCT using two strategies of CMV infection treatment: ganciclovir universal prophylaxis at low doses and preemptive therapy with ganciclovir. The surveillance was based on the monitoring by antigenemia and PCR for detection of CMV and the conclusion was that the patients with a propensity for developing CMV disease can be readily identified and preemptive therapy instituted, avoiding the toxicity related to antivirals and the high cost of universal prophylaxis. Though the antigenemia method is the gold standard to guide previous treatment in HSCT receptors, real-time PCR is emerging as an alternative to substitute antigenemia because it presents several advantages over the antigenemia, including an increased sensitivity for the detection of CMV reactivation, the reliable detection of CMV reactivation during severe neutropenia in the early post-transplant period, the shorter time required for the procedure, and the convenient processing of large numbers of specimens. For this reason Peres et al. (2010) in order to switch the monitoring method from antigenemia to real-time PCR in Bone Marrow Transplant Unit, State University of Campinas (Brazil) determined the cutoff of 418.4 copies/104 PBL (peripheral blood leukocytes) by real-time PCR for preemptive therapy. 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