A total of 535 chemotherapy naive, hospitalised patients (263 male/272 female) scheduled to receive cisplatin (50-120 mg m-2)-containing regimens participated in a randomised, double-blind, parallel group study to evaluate the efficacy and safety of three intravenous dose schedules of ondansetron in the prophylaxis of acute nausea and emesis. One hundred and eighty two patients received a loading dose of 8 mg of ondansetron followed by a 24 h infusion of 1 mg h-1 (group 1); 180 and 173 patients received single doses of 32 mg (group II) and 8 mg (group III) respectively, followed by a 24 h placebo infusion. Complete and major control (less than or equal to 2 emetic episodes) of acute emesis was achieved in 74% of patients in group I, 78% in group II and 74% in group III. Seventy seven per cent of the patients in group I, and 75% of patients in groups II and III respectively experienced no or mild nausea during the 24 h observation period. A retrospective stratification of the efficacy data on the basis of patient gender showed the response rate in females to be significant lower (43% vs 67%; less than 0.001). Ondanestron was well tolerated; mild headache was the most commonly reported adverse event (11% of patients) with a similar incidence in the three groups of patients. In conclusion, a single intravenous dose of 8 mg of ondansetron given prior to chemotherapy is as effective as a 32 mg daily dose given as either a single dose of a continuous infusion in the prophylaxis of acute cisplatin-induced emesis.