This double-blind multicentre study has been carried out in order to confirm the improvement of ondansetron's antiemetic efficacy when combined with a corticosteroid and to determine whether this increased efficacy is maintained over three chemotherapy courses. One hundred and two patients receiving their first course of cisplatin (50-120 mg m-2)-containing chemotherapy were randomised to receive one of the two following treatments: 8 mg OND i.v. injection and 120 mg MPD i.v. injection before chemotherapy, followed 8-12 h later by an 8 mg OND tablet and a 16 mg MPD tablet (oral treatment administered twice daily for 3-5 days): or 8 mg OND plus placebo i.v. injection before chemotherapy, followed by 8-12 h later by an 8 mg OND tablet and placebo p.o. (oral treatment administered twice daily for 3-5 days). The number of emetic episodes (EEs = vomits + retches) and the grade of nausea were recorded. Of the 101 patients studied (efficacy analysis), complete or major control (0-2 EEs) was experienced in 90.4% of patients in the first 24 h in the OND/MPD group compared with 71.4% of patients in the OND group during the first course. This difference in favour of OND/MPD was noted over the three courses and is statistically significant. In the control of delayed emesis (worst day between days 2 and 6) there is a trend in favour of the OND/MDP group during the first course [56.2% vs 43.2% for complete response (no emetic episodes)] which was statistically significant on courses 2 and 3. The global antiemetic control over the course was always in favour of OND/MPD, which leads to a better efficacy maintained over the three courses. Both treatments were well tolerated. The results of this study confirm the increased antimetic efficacy of ondansetron and methylprednisolone in combination in cisplatin-induced acute and delayed emesis which led to a better maintained efficacy over three repeated chemotherapy courses.