• The study end point for statistical purposes will be clearance of CMV viremia at 4 weeks from the start of therapy. Clearance of CMV viremia will be defined as a CMV viral load less than 5,000 copies/ml of whole blood.
  

• All patients will be followed for 6 months after randomization.
  

• To study the effect of preemptive therapy with IV ganciclovir and PO valganciclovir as determined by quantitative CMV PCR.
• To determine the incidence of CMV disease and CMV related mortality following preemptive treatment with oral valganciclovir and IV ganciclovir.
• To compare the incidence of recurrent CMV viremia after treatment with PO valganciclovir to that seen after treatment with IV ganciclovir.
• To determine the toxicity profile of valganciclovir.
• To correlate T-cell subset counts with viral loads.
• To screen for mutations in the UL97 gene in patients who have increasing CMV viral loads after 14 days of treatment.
• To determine if patients treated with PO valganciclovir have ganciclovir drug levels which are equivalent to those seen in historical control subjects treated with PO valganciclovir.

Inclusion Criteria:

• Patients receiving allogeneic peripheral blood stem cell transplant from either a related or unrelated donor at Washington University Medical Center.
• An initial episode of CMV viremia.

• At the time of randomization:

  • ANC greater than or equal to 1000
  • Age greater than or equal to 18
  • Adequate renal function with creatinine clearance greater than 10 ml/min
  • Total bilirubin less than or equal to 3.0

Exclusion Criteria:

• Current GI graft versus host disease grade III-IV
• Development of CMV disease prior to or at the time of the first detection of CMV viremia by PCR
• Uncontrolled emesis or diarrhea (greater than or equal to 4 episodes per day) for 2 consecutive days
• Pregnant or nursing female patient
• Known hypersensitivity to ganciclovir