ObjectiveTo establish guidelines for use of ondansetron.Data sourcesMEDLINE computer search (to July 1993) and information from the manufacturer.Data extractionWe circulated a position paper based on our literature review for comment by clinicians and directors of pharmacy in major teaching hospitals in New South Wales who had an interest in ondansetron.Data synthesisOndansetron is effective in the control of nausea and vomiting occurring 24‐48 hours after highly emetogenic chemotherapy and after radiotherapy. There are no data to support its use in delayed emesis. Combination with dexamethasone may improve emetic control. The most commonly reported adverse effects are headache and constipation. Optimal dose, frequency of dosing and route of administration have not been established. The cost for each inpatient treated successfully is about 3% more than conventional antiemetic therapy.ConclusionsOndansetron shows clinical benefit in the management of acute nausea and vomiting in patients receiving highly emetogenic chemotherapy, those who have responded poorly to other antiemetics after moderately emetogenic chemotherapy, those who have intolerable side effects with conventional antiemetic agents and those receiving radiotherapy to the upper abdomen. It is also marketed for the prevention and treatment of postoperative nausea and vomiting.