We studied the efficacy of two different doses of ganciclovir to prevent cytomegalovirus (CMV) disease in allogeneic hematopoietic stem cell transplantation (HSCT) recipients. We randomly assigned allogeneic HSCT recipients who had CMV infection to receive preemptive ganciclovir therapy with or without induction phase (5 mg/kg twice daily for 1 week). Thirty-two and thirty-six patients were randomized to the standard and the low-dose therapy group, respectively. The median time to CMV antigenemia or viremia clearance was 7 days (3-25 days) in the standard therapy group versus 11 days (3-69 days) in the low-dose therapy group (P = 0.540). The incidence of CMV disease was similar between the two groups (P = 0.366). The Kaplan-Meier estimate of event-free survival by day 180 after HSCT was 76.2% in the standard therapy group versus 66.7% in the low-dose therapy group (P = 0.590). Severe neutropenia (<0.5 x 10(9)/L) was observed in four (12.5%) patients in the standard therapy group versus two (5.6%) patients in the low-dose therapy group (P = 0.314). This study suggests that a low-dose ganciclovir preemptive therapy can be as effective as the standard-dose ganciclovir preemptive therapy for the prevention of CMV disease in allogeneic HSCT recipients.