The prophylactic antiemetic efficacy of ondansetron was evaluated in a randomized, double-blind comparison with droperidol and metoclopramide in 66 patients undergoing general anesthesia for dilatation and curettage. Ten minutes before induction of anesthesia, 22 patients received a single intravenous dose of 8 mg of ondansetron, 22 others received 1.25 mg of droperidol, and the remaining 22 received 10 mg of metoclopramide. Anesthesia was induced with 3.3-5 mg/kg of intravenous thiopental and maintained with 65% nitrous oxide in oxygen and 2%-3% enflurane. Postoperatively, the incidence of vomiting was 13% with ondansetron, 45% with droperidol, and 54% with metoclopramide (P less than 0.05; overall chi 2 test). There was no statistically significant difference in the incidence of nausea among the groups. Postoperative sedation and well-being scores were not significantly different among the groups. We conclude that preoperative prophylactic administration of ondansetron is superior to droperidol or metoclopramide in the prevention of emetic sequelae after general anesthesia for dilatation and curettage.