Silmmary A double-blind, randomized, crossover study was conducted to compare the efficacy and safety of high-dose dexamethasone (Protocol D) with a combination of dexamethasone, metoclopramide and diphenhydramine (Protocol DMD) in the management of chemotherapy-induced nausea and vomiting in cancer patients. All entered patients had received no prior chemotherapy. During the study chemotherapy was administered on an inpatient basis. The majority of patients (94%) were treated with cytotoxic drugs of significant emetogenic activity and 40% of the study group received cis-platin-containing combinations.Of DMD and 9 (15%) found no difference between the two regimens.We conclude that, while the short DMD protocol has an antiemetic activity equivalent in its effectiveness to D, its associated adverse reactions would minimize its usefulness. Therefore, further investigations should be conducted to find a safer and more potent combination of antiemetics suitable for therapy in an outpatient setting.Nausea and vomiting are the most common and potentially grave complications of anticancer therapy (Laszlo & Lucas, 1981;Morran et al., 1979;Seigel & Long, 1981). Moreover, emesis is an important limiting factor in the administration of cytotoxic therapy (Seigel & Long, 1981). Total prevention of chemotherapy-induced nausea and vomiting is paramount in improving patients' acceptance of cytotoxic drugs.Various groups of antiemetics with varying degree of efficacy and modes of action have been tested (Laszlo, 1983;Moertel & Reitemeier, 1969;Moertel et al., 1963;Wampler, 1983). Dexamethasone has been shown to exhibit significant antiemetic activity in the past few years (Aapro & Plezia, 1983;Cassileth et al., 1983Cassileth et al., ,1984Markman et al., 1984). Recently also, in a randomized, double-blind, crossover study, we demonstrated conclusively that high-dose dexamethasone is more effective as an antiemetic and safer than high-dose metoclopramide in patients who are mainly receiving non-cis-platin emetogenic chemotherapy (Ibrahim et al., 1986). However, the dosages and schedule of the antiemetics used in that trial were not suitable for outpatient management.The administration of combinations of antiemetic drugs which would act at different receptor sites should improve their antiemetic potential through complete neuroreceptor blockade (Bruera et al., 1983;Krebs et al., 1985;Mason et al., 1982;Morran et al., 1979). Furthermore, combining two or more antiemetics should minimise the adverse effects produced by the constituent agents given singly in higher doses. The efficacy and safety of a short course of the combination of dexamethasone, metoclopramide and diphenhydramine (Protocol DMD) have been demonstrated recently (Kris et al., 1985). However, the DMD regimen has never been tested in a double-blind and randomized trial against the well established antiemetic protocols.We now present the outcome of a randomized, doubleblind, crossover study comparing the effectiveness of highdose dexamethasone (Protocol D) with a short...