Peri-operative nausea and vomiting (PONV), remain a considerable problem. Ondansetron is being promoted currently as the drug of choice for the prevention and treatment of PONV. Experiments to investigate efficacy of ondansetron in PONV have been made with placebo or single doses of other drugs, e.g. metoclopramide, and often with different anaesthetic regimes with different emetic potential. This study investigated the relative benefits, in the prevention of PONV, of ondansetron compared with metoclopramide used at a dose higher than used in previous studies. Ninety-six patients undergoing minor gynaecological surgery were randomized to receive either ondansetron 4 mg or metoclopramide 0.4 mg kg−1. The patients were then assessed in the recovery room, in the day ward prior to discharge and the following day for the occurrence of PONV. Emetic symptoms occurred in similar proportions of patients who received ondansetron and metoclopramide. Nausea scores were similar between the groups in the recovery ward and 24-h follow-ups but there were higher post-operative nausea scores in the ondansetron group in the day ward (P = 0.001). There were no significant side effects due to either drug. We conclude that moderate dose metoclopramide is an effective alternative to ondansetron in the control of PONV.