This prospective, randomized, double-blinded study was performed to evaluate the effects of intravenous metoclopramide and ranitidine on preoperative gastric contents in outpatients receiving intravenous anesthesia for laparoscopic gynecologic surgery. Fifteen minutes before the induction of anesthesia, the Z-M group (n=20) received 50 mg ranitidine and 10 mg metoclopramide intravenously and the control group (n=20) received the same volume of normal saline. Before the surgery, a 14-F multiorifice nasogastric tube was inserted to aspirate the gastric contents of patients under sedation with propofol and midazolam. The mean pH values of the gastric fluid were 2.7 +/- 2.0 (SD) [median 1.6 (range: 1.2-7.2)] in the control group, and 6.1 +/- 1.9 [median 6.8 (range 1.4-7.8)] in the Z-M group. The mean aspirated volumes (mL) were 15.3 +/- 10.4 (SD) [median 11.0 (range: 5.0-44.0)] in the control group, and 6.9 +/- 10.0 (SD) [median 4.5 (range: 0-38.0)] in the Z-M group. There were significantly more high-risk (gastric fluid volumes > 25 mL and pH < 2.5) patients in the control group (4/20, 20%) than in the Z-M group (1/20, 5%). In conclusion, intravenous prophylactic ranitidine and metoclopramide may be an easy and useful method to decrease the volume while increasing the pH of gastric contents, and therefore may reduce the number of patients at risk for aspiration pneumonitis in ambulatory laparoscopic procedures who receive an anesthesia.