• Upper GI endoscopy (EGD), symptoms based on subject's daily diary and investigator's assessment. [ Time Frame: Every 4-8 weeks. ] [ Designated as safety issue: No ]
  

• Adverse events, ECGs, laboratory evaluations (hematology, blood chemistry, urinalysis, serum gastrin), physical examinations, vital signs. [ Time Frame: Every 4-8 weeks. ] [ Designated as safety issue: Yes ]
  

KEY INCLUSION CRITERIA:

• Male or female, ages 18 to 75 years.
• History of GERD symptoms for at least 3 months immediately before screening.
• Heartburn for at least 2 days a week for at least 1 month before screening.
• Esophageal erosions of LA Grades C or D based on EGD taken within 14 days prior to enrollment.
• Subjects who are H. pylori negative based on a screening test.
• Females should be either of non-childbearing potential or of childbearing potential. Females of childbearing potential must have negative pregnancy tests prior to randomization. Female subjects of childbearing potential must agree to use medically acceptable methods of contraception.
• Subjects must be able to read, write, and understand the language of the symptom diary.

KEY EXCLUSION CRITERIA:

• Current or a history of esophageal motility disorders.
• Current or a history of Barrett's esophagus. Current esophageal strictures or esophagitis (known or suspected to be due to etiology other than GERD such as infection or medications).
• Current or a history of Zollinger-Ellison syndrome and other acid hypersecretory conditions, or current gastric or duodenal ulcer.

Current or a history of cancer, with the exception of fully excised skin basal cell carcinoma.

• Inflammatory bowel disease.
• Unstable diabetes mellitus.
• History of esophageal, gastric and duodenal surgery except simple suturing of an ulcer.
• Subjects who require daily use of nonsteroidal anti-inflammatory drugs (NSAIDs), oral steroids (>= 20 mg/day prednisone or equivalent), or aspirin (> 325 mg/day).