Alizapride is a methoxy-2-benzamide derivative three times more potent than its parent compound, metoclopramide, as an antagonist of apomorphine-induced emesis in dogs. The antiemetic activity of alizapride plus dexamethasone (DXM) was compared with that of placebo plus DXM in a randomized, double-blind, crossover study in cancer patients receiving cisplatin (DDP). Alizapride, given at the maximally tolerated dose of 4 mg/kg x 5, or placebo was given in a sequence determined by randomization during two successive, identical courses of antitumor chemotherapy. The antiemetic treatment was given 30 min before and 1.5, 3.5, 5.5, and 7.5 h after starting. DXM, in a dose of 12 mg, was given IV with the first administration of alizapride or placebo. A total of 39 patients completed the two courses of chemotherapy. The severity of gastrointestinal symptoms was influenced by previous treatment but not by the treatment sequence. Although our overall results suggest that alizapride does not add to the activity of DXM against DDP-induced amesis, a statistically significant difference favoring alizapride plus DXM was found among patients with the lowest gastrointestinal tolerance to DDP: women, patients under 50 years of age, and patients pretreated with chemotherapy including DDP and non-DDP agents. Side effects consisted of orthostatic hypotension, which was symptomatic in two patients, and a single occurrence of severe extrapyramidal syndrome. We conclude that alizapride is more active than placebo when combined with DXM for DDP-induced emesis in patients at high risk of severe nausea and vomiting. The severity of the side effects in this study indicates that a dose reduction of alizapride might be appropriate for further studies.