Study subjects will be admitted to the Temple Clinical Research Center for the duration of the study. Appendix I has the study time line. Study subjects will arrive at the CRC at 6:00 A.M. on study day 1. Female subjects will have a urine pregnancy test performed. Blood tests will be obtained for salicylate and alcohol levels. Each study subject will receive a single dose of study drug (rabeprazole or placebo) at 7:00 A.M. on study days 1, 2 and 3—one hour before breakfast on days 1 and 3 and 90 minutes before breakfast on study day 2. All research subjects will receive aspirin (ASA), 325 mg tablets as 2 tablets with 8 oz. water every 4 hours at 8:30 A.M., 12:30 P.M., 4:30 P.M., 8:30 P.M., 12:30 A.M. and 4:30 A.M. daily for study days 1, 2 and 3 (a total of 3900 mg aspirin per day). Esophagogastroduodenoscopy will be performed at 8:00 A.M. on the mornings of days 2 and 4; that is, 24 hours and 72 hours after initiation of aspirin and test drug. During each endoscopy, the maximum number of submucosal hemorrhages and erosions in an endoscopic field from the anterior and posterior walls of the antrum will be counted. In addition, a Lanza score will be assigned for each endoscopic examination (Appendix II). Endoscopic photographs will be obtained for each endoscopic examination. A blood sample will be obtained at 7:00 A.M. on study days 2, 3 and 4 for measurement of hemoglobin and serum salicylate. Meals will be standardized as follows for each day of the study: