Background and objective: In cases of aspiration of gastric contents the risk of pneumonitis is dependent on the pH and volume of the gastric contents. Omeprazole and rantidine each decrease gastric volume and increase gastric pH. We evaluated the efficacy of preoperative administration of omeprazole (60 mg) or ranitidine (150 mg) in the prophylaxis of aspiration pneumonitis. Methods: Data were obtained from 75 elective female surgical patients randomly allocated to one of three groups, who received either omeprazole 60 mg orally, or ranitidine 15 0 mg orally, or neither, on the evening prior to, and on the morning of, surgery. Gastric volume and pH was measured using blind aspiration. Results: Both pH <2.5 and volume >25 mL were present in none of the patients in either the ranitidine or omeprazole groups, compared to 15 of 25 control patients (P < 0.0001). Conclusions: Preoperative oral administration of omeprazole (60 mg) or ranitidine G 50 mg) reduced residual gastric content volume and increased pH > 2.5, possibly reducing the effects of pulmonary aspiration of gastric contents.Background and objective: In cases of aspiration of gastric contents the risk of pneumonitis is dependent on the pH and volume of the gastric contents. Omeprazole and rantidine each decrease gastric volume and increase gastric pH. We evaluated the efficacy of preoperative administration of omeprazole (60 mg) or ranitidine (150 mg) in the prophylaxis of aspiration pneumonitis. Methods: Data were obtained from 75 elective female surgical patients randomly allocated to one of three groups, who received either omeprazole 60 mg orally, or ranitidine 15 0 mg orally, or neither, on the evening prior to, and on the morning of, surgery. Gastric volume and pH was measured using blind aspiration. Results: Both pH <2.5 and volume >25 mL were present in none of the patients in either the ranitidine or omeprazole groups, compared to 15 of 25 control patients (P < 0.0001). Conclusions: Preoperative oral administration of omeprazole (60 mg) or ranitidine G 50 mg) reduced residual gastric content volume and increased pH > 2.5, possibly reducing the effects of pulmonary aspiration of gastric contents.