A double-blind, randomised, placebo-controlled trial was conducted to compare the efficacy of metoclopramide with the 5-HT3 antagonist, ondansetron, for the prevention of postoperative emesis in children undergoing elective strabismus surgery. None of the children received any premedication and a similar anaesthetic technique was used for all. Ondansetron 0.15 mg.kg-1, metoclopramide 0.25 mg.kg-1 or saline placebo were administered following intravenous catheter placement. Episodes of emesis were recorded for the first 24 h for the intervals of 0-2, 2-6 and 6-24 h. The incidence of emesis in the first 24 h was observed to be 71.7% in the placebo group, 34.4% in the ondansetron group (p < 0.001) and 61.4% in the metoclopramide group (p = NS). The severity of vomiting was less in the ondansetron group as compared with metoclopramide (p < 0.01) and placebo (p < 0.001). Recovery room scores were comparable in all the groups. No serious side-effects were observed in the ondansetron group. We conclude that prophylactic ondansetron is effective and superior to metoclopramide in the prevention of postoperative emesis in children following elective strabismus surgery.