Human cytomegalovirus (HCMV) has remained a major cause of morbidity and mortality following allogeneic bone marrow or peripheral blood stem cell transplantation (SCT). The most reliable virological predictive marker for disease development is the presence of HCMV viremia. It has been further recognized that viral load, and viral load kinetics are important determinants of pathogenesis. Prior to the preventive use of antiviral agents, CMV disease occurred in 15-45% of at-risk patients and carried a high mortality rate. In the last decade, major advances in the prevention of CMV disease have occurred with the application of pp65 antigenemia and qualitative/quantitative polymerase chain reaction (PCR) assays for the rapid and sensitive diagnosis of HCMV infection, combined with preemptive antiviral treatment targeted to patients with viremia. The prevalence of early CMV disease has declined to 3% to 6% with intense antiviral drug use. All antiviral drugs currently used for the treatment of systemic HCMV infection, including ganciclovir, foscarnet, and cidofovir, target the HCMV DNA polymerase. Ganciclovir is the most widely used drug for preemptive treatment. However, ganciclovir treatment is often complicated by bone marrow toxicity with the occasional development of potentially life-threatening thrombocytopenia, granulocytopenia, and graft failure, associated with secondary bacterial and fungal infection. Another limitation of preemptive ganciclovir therapy is the requirement for intravenous administration. The currently available oral valganciclovir is not yet approved for preemptive therapy in SCT recipients, and is associated with high treatment cost. Additionally, prolonged or repeated ganciclovir treatment may lead to the development of drug resistance. The use of foscarnet and cidofovir is limited by considerable nephrotoxicity, low oral bioavailability, and high cost. Thus, there is an increasing need for new effective non-toxic, low-cost anti-HCMV drugs with high oral bioavailability.