The question of whether or not prolonged exposure to ganciclovir will result in an increase in the incidence of resistant CMV strains has not been answered. There is also a theoretical increase in the risk of selection pressure for resistant CMV when the lower dose of valganciclovir (450 mg) is used. This proposal will document the emergence of ganciclovir-resistant strains of CMV in high-risk kidney, pancreas, or combined kidney/pancreas transplant patients receiving long-term suppressive therapy with Valcyte™ and will also address the issue of selection pressure by randomizing for low and high dose valganciclovir prophylaxis. Emergence of resistance will be defined as detection of a resistance-conferring mutation in the UL97 (phosphotransferase) or UL54 (DNA polymerase) open reading frame of detectable CMV.