This multi-centre randomized study assessed the bioavailability of ganciclovir in patients undergoing alemtuzumab-based reduced intensity conditioning (RIC) haematopoietic stem cell transplantation (HSCT) after oral administration of valganciclovir. Patients were randomized to 2 groups receiving either oral valganciclovir (900 mg twice daily) or intravenous ganciclovir (5mg/kg twice daily) for 14 days. Twenty-seven patients were recruited and 18 patients (67%) completed allocated treatment resulting in clearance of cytomegolovirus (CMV) DNA load at a median of 14 days. The bioavailability of ganciclovir from valganciclovir was 73% (95% CI: 34-112%). The average exposure in the valganciclovir group (36.9+/-14.9 microg h/ml) was higher than the ganciclovir cohort (27.9+/-7.5 microg h/ml). When compared with intravenous ganciclovir, oral valganciclovir had high bioavailability in patients undergoing alemtuzumab-based RIC HSCT.