Inclusion Criteria:

1. Subjects, 18-65 years of age, inclusive, male or female, of any race, who are willing to undergo testing at the study center.
2. Female subjects must not be able to conceive by reason of surgery, radiation, 2 years past the onset of menopause, or an approved method of contraception (e.g., IUD, oral contraceptives for at least one cycle, implant, or double barrier method). Female subjects of childbearing potential must have a negative serum pregnancy test at screening and a negative urine pregnancy test before medication is dispensed.
3. Subjects must have a negative result on the screening for H. pylori by serology, and no history of H. pylori eradication.
4. Subjects must have history of GERD with or without antacid use.
5. Subjects must be able to tolerate nasogastric tube placement.

Exclusion Criteria:

1. History of gastric surgery, fundoplication or vagotomy.
2. Pyloric stenosis Barrett's esophagus or esophageal stricture.
3. Treatment with a histamine H2-receptor antagonist, prostaglandin, or sucralfate within 14 days before enrollment into this study.
4. Treatment with rabeprazole, omeprazole, lansoprazole, pantoprazole, esomeprazole, prokinetic agent, or bismuth subsalicylate within 30 days before enrollment into this study.
5. Concurrent serious systemic disorders, including renal insufficiency and hepatic insufficiency.
6. Subjects with neoplasia or undergoing treatment for cancer (e.g., chemotherapy, radiation.
7. Any condition associated with poor subject compliance (e.g., alcohol abuse, drug abuse).
8. History of clinically significant abuse of alcohol defined as (1) patterns of alcohol intake consistent with disruption of normal function in society; (2) history of, or current existence of any indication of difficulty in abstaining from alcohol for the required duration of the present protocol; (3) use of any alcohol within one day of any study period.
9. Subjects who have received any investigational agent within the previous 30 days.
10. Inability of subject to return for scheduled visits.
11. Subjects who, in the opinion of the investigator, are poor medical or psychiatric risks for therapy with an investigational drug.
12. History of any hypersensitivity reaction to rabeprazole, pantoprazole or any of their inactive ingredients.
13. Any significant evidence at screening of endocrine, cardiovascular, and/or pulmonary disorder.
14. Any predisposing condition that might interfere with the absorption, distribution, metabolism, or excretion of drug, or a history of abnormal bleeding tendencies or thrombophlebitis.
15. History of HIV, hepatitis B, or hepatitis C infection.
16. Subjects who are pregnant or likely to become pregnant during the course of this study.