Thirty four patients who were receiving carboplatin 400 mg/m2 for advanced epithelial ovarian cancer were treated with ondansetron antiemetic prophylaxis. Ondansetron was given as 4 mg oral +4 mg iv 30 minutes prior to carboplatin followed by 8 mg oral tds for 5 days. Of the evaluable patients complete or major control of emesis on day one was achieved in 94% of previously untreated patients and 81% of patients refractory to conventional antiemetic therapy. For the 5 day period as a whole 88% of untreated patients and 69% of those with refractory emesis reported complete or major control of nausea and vomiting. Fifteen patients noted no side effects with mild headache (30%) and constipation (21%) the most frequent problems in the remainder. Ondansetron is effective antiemetic prophylaxis for carboplatin chemotherapy and should allow the majority of these patients to be managed on an out-patient basis.