We studied the practice patterns regarding intravenous (i.v.) ondansetron in children receiving stem cell transplants (SCT) at The Children's Hospital, Boston to identify cost efficiencies. The pharmacy provided information on material and preparation costs on 36 patients who received i.v. ondansetron during 41 SCT in 1995. We examined the effects of frequency, duration, and route of administration on costs. There were 498 days of ondansetron administration costing $49,083 (95$). Tremendous variation existed in frequency and duration with one third receiving i.v. ondansetron once daily, despite published evidence of equivalence of once a day and divided dosing. A switch to once daily i.v. dosing for all patients would have resulted in >/=28% savings. The median duration of use was 11 days (range 1-48); placing a cap for 7-10 days based on the length of SCT conditioning regimens, would produce savings of 48-60% over current use. By shifting administration route from i.v. to oral, a savings of 67% over current use, without a cap on duration, would be realized. Identifying areas for cost savings can be achieved after thorough analysis of all the component costs. We demonstrated that significant cost reductions could be realized by simple changes in prescribing practices without jeopardizing efficacy. These savings are achieved by standardizing dosing interval, route of administration and duration of treatment without altering daily dosage or access to an effective antiemetic. Bone Marrow Transplantation (2000) 25, 553-557.