In a prospective randomized study, 60 children between 1 and 8 years of age in three groups received no premedication, 10 mg kg-1 cimetidine orally or 40 mg kg-1 cimetidine rectally for prophylaxis of acid aspiration syndrome 120-180 min before induction of anaesthesia. The pH of the stomach contents was above 2.5 in both cimetidine groups. The aspirated gastric volume was significantly reduced with rectal cimetidine compared to the other groups. Rectal cimetidine proved to be the more effective drug for prophylaxis of acid aspiration syndrome in paediatric anaesthesia.