The safety and efficacy of ondansetron were evaluated for the treatment of postoperative nausea and vomiting after laparoscopic surgical procedures. Seventy-one healthy, consenting outpatients were randomly assigned to one of two treatment groups according to a double-blind, placebo-controlled protocol. A standardized anesthetic technique consisting of alfentanil-thiopental-succinylcholine for induction and alfentanil-nitrous oxide-succinylcholine for maintenance of anesthesia was used. Patients in whom postoperative nausea and/or vomiting developed and persisted for greater than or equal to 10 min received equivolemic intravenous injections of either ondansetron (8 mg) or saline (placebo) over a 2-5 min period. Ondansetron significantly decreased the posttreatment nausea scores (vs placebo) without increasing sedation or producing changes in cardiorespiratory parameters. In the placebo-treated group, 92% of the patients experienced subsequent episodes of vomiting in the postanesthesia care unit compared with 51% of the patients in the ondansetron group. Finally, only 43% of the ondansetron-treated patients required a "rescue" antiemetic compared with 86% in the placebo group. Thus, ondansetron (8 mg IV) was associated with a decreased incidence of nausea and vomiting after outpatient laparoscopic procedures.