A double-blind, randomised, placebo-controlled study was performed to assess the antiemetic efficacy of ondansetron in women receiving morphine from a patient-controlled analgesia system after total abdominal hysterectomy. Sixty-six ASA grade 1 or 2 patients scheduled for total abdominal hysterectomy were randomly allocated into one of two groups. All patients received a standardised anaesthetic and postoperative patient-controlled analgesia regimen. Group 1 received ondansetron 4 mg at induction of anaesthesia, repeated 8 h later. Group 2 received saline as a placebo at the same times. Pain scores, nausea scores, episodes of vomiting, use of rescue antiemetics and recollection of nausea and vomiting were not different between the groups. Only 15% of patients who received ondansetron and 30% of patients who received the placebo recorded no nausea or vomiting in the first 24 h. We conclude that ondansetron, in the dose studied, does not reduce nausea and vomiting in women receiving morphine from a patient-controlled analgesia system after total abdominal hysterectomy.