We report the results of two clinical trials in which patients receiving either doxorubicin (Adriamycin)/cyclophosphamide or cis-platinum cytotoxic chemotherapy were assigned at random either a single or a combination antiemetic treatment. The aim of each trial was to assess whether combination antiemetic therapy would result in improved efficacy. Sixty patients commencing doxorubicin/cyclophosphamide therapy were divided in two random groups to receive either haloperidol or haloperidol plus amitriptyline, and 80 patients commencing cis-platinum therapy were divided at random to receive either metoclopramide or metoclopramide plus promethazine. No statistically significant differences were apparent between single and combination antiemetic regimens in either of the two treatment groups. Antiemetic agents were generally well-tolerated, but minor side effects were common. The failure of our combination antiemetic regimens to intensify the proven antiemetic efficacy of single agents emphasises the need for re-evaluation of currently used antiemetic agents and their dosage schedules.