BACKGROUND: Children undergoing general anesthesia are at increased risk of aspiration pneumonia. Cimetidine and ranitidine, specific histamine (H2-receptor) antagonists, markedly reduce the acidity and volume of gastric content when given 2 3h preoperatively. A newer compound, famotidine, is a more specific antagonist that has no inhibitory effect on the drug metabolizing microsomal enzyme systems of the liver (cytochrome P-450), in contrast to cimetidine. An additional clinical advantage is a possible longer duration of action. The aim of this study is to evaluate the lowest effective dose of famotidine on gastric pH and volume in children. METHODS: Fifty-five children, aged 2 to 14 years (ASA physical status I-II) were divided into four groups (Group I:placebo, normal saline 10 ml, Group II:famotidine 0.1 mg/kg, Group III:famotidine 0.15 mg/kg, Group IV:famotidine 0.2 mg/kg.). Doses were administered intravenously 2 or 3 hours before the operation. Following induction with oxygen, enflurane and pentothal sodium, anesthesia was maintained with N2O/O2 and enflurane. A nasogastric tube was passed into the stomach and the gastric contents were aspirated in a uniform manner. Gastric volume was recorded and pH values were measured with pH meter. The incidence of high risk for aspiration pneumonia, defined as gastric pH < 2.5 and gastric fluid volume > 0.4 ml/kg of gastric juice, was measured in all groups. RESULTS: In the placebo group, 10 of 13 children (77%) had a pH < 2.5 and gastric volume > 0.4 ml/kg. Group II (famotidine 0.1 mg/kg) was not found to produce a significant increase in the gastric pH. Groups III and IV (famotidine 0.15 mg/kg and 0.2 mg/kg) were found to produce a significant increase in the gastric pH. The gastric juice volume was reduced in all famotidine groups, but was not statistically significant compared with the placebo group. The incidences of high risk for aspirationpneumonitis decreased in all famotidine groups. CONCLUSIONS: The results suggest that the preoperative intravenous administration of famotidine 0.15 mg/kg is enough to decrease both gastric juice acidity and volume in this high-risk group.