Metoclopramide may be used to stimulate gastric emptying when anaesthetizing children for emergency operations. Unfortunately, metoclopramide is associated with extrapyramidal side effects. Erythromycin, a motilin receptor agonist, is a prokinetic agent but its use has been little investigated in children. This randomized double-blind study compared the effects of premedication with oral metoclopramide 0.15 mg kg(-1) or erythromycin 1 mg kg(-1) on gastric emptying in 80 children undergoing tonsillectomy. Pre-operative fluids, premedication and anaesthetic technique were standardized and gastric volume was measured with an orogastric tube. Post-operative nausea and vomiting was recorded. Metoclopramide and erythromycin produced similar gastric volumes (0.29 and 0.24 ml kg(-1)) and there was no difference in post-operative vomiting. In the erythromycin group there were more patients with negative aspirates (45.9%) than in the metoclopramide group (35.1%), but the difference was not statistically significant. These results indicate that erythromycin may be as effective as metoclopramide as a prokinetic agent.