High-dose intravenous (IV) metoclopramide has shown efficacy with few side effects for the treatment of nausea and vomiting on the day of cisplatin administration. From November 1984 to January 1986, two randomized trials in an antiemetic study were conducted. In trial I, the antiemetic effect of a short course of high-dose dexamethasone was compared with that of high-dose metoclopramide in 29 patients with lung cancer receiving chemotherapy containing cisplatin (80 mg/m2 IV) in a randomized controlled trial. Dexamethasone was given IV at a dose of 16 mg 1/2 hr before and 8 mg, 1 1/2, 3 1/2 and 5 1/2 hr after cisplatin. Metoclopramide was given IV at a dose of 2 mg/kg, 1/2 hr before and 1 1/2, 3 1/2 and 5 1/2 hr after cisplatin. Major emetic control (0-2 episodes of vomiting) during the 24 hr after cisplatin administration was achieved in 55% (6/11) and 67% (12/18) of the patients receiving dexamethasone and metoclopramide, respectively, without serious toxicity. The duration of nausea or anorexia was similar for the two treatment groups. In trial II, the combination of metoclopramide and dexamethasone was compared with metoclopramide alone to assess the additive antiemetic effect of the two drugs in 23 patients with lung cancer receiving cisplatin at a dose of 120 mg/m2 IV in a randomized cross-over study. A major antiemetic response was observed in 27% (3/11) and 92% (11/12) of the patients receiving metoclopramide alone and metoclopramide plus dexamethasone, respectively (p less than 0.005). The duration of nausea and anorexia was similar for the two treatment groups. Patients tended to prefer the combination of metoclopramide and dexamethasone; however, the difference was not statistically significant (p = 0.14) in the small number of patients entered in this study. Despite excellent control of acute chemotherapy-induced emesis, 45% of 52 patients experienced delayed nausea and vomiting more than 24 hr after cisplatin administration even among those who had had an excellent short-term response to the antiemetic agents.