Patients undergoing major abdominal surgery are at highest risk for developing postoperative ileus (POI), occurring in nearly all cases. Signs and symptoms of POI may include abdominal distention, bloating, persistent abdominal pain; nausea and/or vomiting; delayed passage or inability to pass flatus or stool; and inability to tolerate a solid diet. This study will test the ability of alvimopan 6 mg or 12 mg given 2 hours before the scheduled start of surgery to hasten the recovery of GI function in patients undergoing major abdominal surgery (bowel resection or abdominal hysterectomy).