A double-blind, randomized crossover trial was carried out in 44 cancer patients receiving chemotherapy with cis-platinum to compare the anti-emetic effectiveness and tolerance of alizapride and domperidone given in high dosage. Patients received 5 administrations of either 4 mg alizapride/kg body weight or 0.6 mg domperidone/kg during a chemotherapy session and then the alternative anti-emetic during the next session. Treatment order was randomized. Patients were followed-up for 12 hours and details recorded of the total time during which there was some nausea, the duration of mild and severe nausea, and the number of episodes of mild and severe vomiting. A note was also made of the duration of mild and moderate sedation, and the incidence and severity of any other side-effects either probably or possibly related to anti-emetic medication. The investigator gave an overall assessment of the severity of nausea and vomiting experienced during each chemotherapy session and an opinion on the comparative effectiveness of the two anti-emetics. At the end of the two sessions, patients were asked to state a preference, if any, for one or other treatment and to select which they would like to have for their next chemotherapy session. The results showed that whilst both alizapride and domperidone appeared to be equally effective in limiting mild nausea, alizapride was significantly better in preventing severe nausea and episodes of vomiting. In those cases where a positive choice between treatments was made, alizapride was considered to be significantly better than domperidone by the investigator and more patients preferred alizapride and would select it for their next session.(ABSTRACT TRUNCATED AT 250 WORDS)