Patients at risk of CMV disease (D+R-, D+R+, D-R+), who are being treated prophylactically with Valcyte® (commercially available tablets), after their first or second kidney transplant and who have adequate renal and hematological function will be eligible for the study. Screening may be at any time after transplantation provided that follow-up procedures can be completed during the scheduled time of prophylaxis. The first dose of study drug may be between 1 and 14 days after screening provided the transplant has stabilized, stable serum creatinine and steady-state kinetics of ganciclovir and calcineurin inhibitor therapy have been attained. Follow-up will take place 7- 14 days after last dose of study drug administration; therefore the duration of the study will be up to 5 weeks.