['This study tested the hypothesis that the antiemetic effects of a combination of ondansetron and propofol were superior to propofol alone in children undergoing tonsillectomy surgery.', 'A prospective, randomized, double-blind, placebo-controlled study design was employed. Young children underwent mask induction with halothane, nitrous oxide and oxygen and then had i.v. access established: older children had i.v. induction with propofol. All patients received 0.3 mg x kg(-1) mivacurium and 2-4 microg x kg(-1) fentanyl i.v. and 30 mg x kg(-1) acetaminophen pr to a maximum dose of 650 mg. Following induction, patients received either 100 microg x kg(-1) ondansetron or placebo. Anaesthesia was maintained with 120-140 microg x kg(-1) x min(-1) propofol, nitrous oxide and oxygen to maintain vital signs within 20% of baseline. After surgery, in all patients the tracheas were extubated in the operating room without use of neuromuscular reversing agents. Episodes of emesis were recorded by PACU nurses for four to six hours. A telephone interview on the following day was also used for data recovery. Groups were compared in relation to age using the Mann-Whitney test, and with respect to sex and number of episodes of vomiting using the Fisher Exact Test.', 'Three of the 45 patients who received ondansetron vomited (6.7%), whereas 10 of the 45 patients who received placebo vomited (22.2%). (P = 0.035)'] Does ondansetron with propofol reduce the incidence of emesis in children following tonsillectomy?