The anti-emetic effects, safety and usefulness of ondansetron, a 5-HT3 receptor antagonist, given orally once daily for 3-5 consecutive days, were investigated in patients receiving a high single dose (greater than or equal to 50 mg/m2 or 75 mg/body) or lower multiple doses (greater than or equal to 15-20 mg/m2/day for 3-5 consecutive days) of cisplatin. Ondansetron 4 mg was administered orally once daily for 3-5 consecutive days. Efficacy rates in controlling nausea and emesis over the 3-5 days were 77.3% (17/22 cases) and 66.7% (6/9 cases) in patients receiving a high single dose and lower multiple doses of cisplatin, respectively. Side effects were observed in 2 cases (headache and elevation of blood pressure in one case and only headache in the other case.). Abnormality in clinical laboratory findings was observed in 1 case. From the above, ondansetron, showing high efficacy by oral administration 4 mg once daily for 3-5 consecutive days, without any problem in safety, was considered to be a useful anti-emetic agent.