Thirty-seven patients with advanced incurable malignancies who were receiving their first course of cisplatin (2 90 mg/mz bolus), alone or in combination with other antineoplastic agents, were entered in this randomized, double-blind study to determine the antiemetic efficacy of the addition of high-dose dexamethasone to lorazepam plus metoclopramide. All patients received lorazepam (1.5 mg/mz) and metoclopramide (2.0 mg/kg) intravenously (IV) 30 minutes before cisplatin, with the same dose of metoclopramide repeated 1.5, 3.5, 6.5, and 9.5 hours after the 30minute cisplatin infusion. Patients were randomized to receive dexamethasone (0.5 mg/kg) or placebo by slow bolus injection 30 minutes before cisplatin. All patients were hospitalized for 24 hours and evaluated by observation after cisplatin and a patient questionnaire before discharge. Eighteen patients received metoclopramide and lorazepam without dexamethasone: six (33%) reported no vomiting and four (22%) reported no nausea or vomiting. Nineteen patients also received dexamethasone: 14 (74%) had no vomiting and 13 (68%) reported no nausea or vomiting. These differences were statistically significantly different ( P = 0.013 and 0.005, respectively). The side effects attributable to the antiemetic regimen were somnolence (loo%), confusion (a%), and diarrhea (46%), and were the same in both arms. Dexamethasone significantly improved the antiemetic efficacy of metoclopramide plus lorazepam without adding toxicity. This three-drug combination gave a high rate of control of acute emesis induced by high-dose cisplatin.