One hundred and eleven patients receiving conditioning regimens for hematopoietic stem cell transplantation (HSCT) were administered a single intravenous dose (40 micrograms/kg) of granisetron before chemo-radio therapy. The efficacy of the drug was assessed every 24 hours, rating the control of nausea and vomiting as complete, major, minor or failure. On day 1, 23 of 48 patients (47.9%) who received cyclophosphamide (60 mg/kg/day), achieved control of emesis with complete or major response. On day 2, 17 of 47 patients (36.2%) achieved control emesis. During total body irradiation (TBI) (10 approximately 12 Gy/2 approximately 3 days), 21 of 33 patients (63.6%) achieved control of emesis on day 1 and 22 of 32 patients (68.6%) achieved control of emesis on day 2. During melphalan administration (60 approximately 100 mg/m2/day), 20 of 28 patients (71.4%) achieved control of emesis on day 1. Adverse effects were observed in seven patients but were not serious. We concluded that granisetron has a major role in preparation for HSCT.