The object of the study was to determine whether dexamethasone improved the efficacy of the serotonin receptor (5-HT3) antagonist granisetron in controlling acute (within 24 h) emesis in cancer patients receiving high-dose cisplatin chemotherapy and to ascertain whether continuation of granisetron after 24 h reduces the occurrence of delayed emesis. This randomised, double-blind, multicentre, three-arm study was conducted at 21 medical centres. A group of 292 nausea- and emesis-free patients with cancer, who had never had chemotherapy and were scheduled to receive at least 50 mg/m2 cisplatin, were given 3 mg granisetron i.v. in a 15-min infusion with or without 10 mg dexamethasone i.v. completed 5 min prior to high-dose cisplatin and 1 mg granisetron p.o. at +6 h and +12 h. Primary study end-points were control of emesis and nausea. Patients completed a self-report diary every 6 h for the first 24 h. At the end of the 24-h period, the patients who received dexamethasone had a significantly higher complete protection rate from emesis (64% compared to 39%) than those who received no steroid. Similarly, the dexamethasone-treated group had a significantly higher complete plus partial (0-2 emetic episodes) protection rate (84% compared to 64%). This study shows that dexamethasone markedly enhances the antiemetic efficacy of granisetron for acute-onset emesis in high-dose cisplatin chemotherapy.