Gastric pH values were studied prior to, and up to, ninety minutes after an intravenous injection of cimetidine 200 mg given before general anaesthesia, in twenty surgical patients, all with a gastric pH less than 3.5. At thirty, sixty and ninety minutes, sixteen, eighteen and twenty patients had a gastric pH greater than 3.5 respectively. In conclusion, the results of the present study indicate that cimetidine 200 mg given intravenously 90 minutes before surgery will reduce the hazard of chemical pneumonitis should stomach content be aspirated.