A multicentre randomised, double-blind parallel group study has been carried out in order to confirm the antiemetic efficacy of orally administered ondansetron. A total of 259 chemotherapy-naive breast cancer patients treated with a 5-fluorouracil, doxorubicin, cyclophosphamide (FAC) or 5-fluorouracil, epirubicin, cyclophosphamide (FEC) regimen were randomly assigned to ondansetron (OND) 8 mg tablet or alizapride (ALI) 150 mg intravenous (i.v.) injection, prior to chemotherapy. These treatments were then followed by OND 8 mg tablet or ALI 50 mg tablet, respectively, 8 to 12 h later. Oral treatment was then continued twice a day over 3-5 days. The number of emetic episodes (EE = vomits+retches) and the grade of nausea were recorded; quality of life was assessed using a specific questionnaire. Of the 254 patients analysed for efficacy, complete or major control (success: 0-2 EE) over the 24 h following start of chemotherapy was obtained in 81% of the OND group compared with 47% of the ALI group (P < 0.001). A significant difference in favour of OND was also observed for nausea (P < 0.0001). For on days 2 to 4 emesis, the arm containing OND was superior to that with ALI (worst day analysis): 77% success versus 63% (P < 0.002). The overall control of emesis (from day 1 to day 4) was better with OND (64% patients success in the OND group versus 41% in the ALI group; P < 0.0001). At the end of the study the number of patients wishing to receive the same anti-emetic treatment for their next course was 83% for OND compared with 54% for ALI (P < 0.0001). In terms of quality of life in relation to emesis phenomena, OND was significantly superior to ALI (P = 0.04). Both treatments were well tolerated. In the prevention of the prolonged emesis induced by FAC/FEC-type emetogenic chemotherapy, orally administered OND was superior to ALI, given as an i.v. injection and followed by tablets.