Inclusion Criteria:

   - Patients included in the study will have a hematologic malignancy (any stage or grade)
   for which they are undergoing preparation for allogeneic HSCT; participants in the
   study will be restricted to those undergoing HSCT under reduced-intensity protocols
   9924 and 9907

   - No limitations exist for type or amount of prior therapy

   - No restrictions or requirements will be placed on race

   - No restrictions will be made based on life expectancy

   - Patients will not be evaluated based on Eastern Cooperative Oncology Group (ECOG) or
   Karnofsky performance status (KPS)

   - No restrictions will be made based on organ or marrow function

   - Patients will be included only if they have the ability to understand and the
   willingness to sign a written informed consent document

Exclusion Criteria:

   - Patients with a history of gastric bypass surgery or inflammatory bowel disease

   - Patients with a history of or current bowel obstruction

   - Patients actively enrolled on any other GVHD prevention trial

   - Patients with known fructose intolerance

   - Any physical or psychological condition that, in the opinion of the investigator,
   would pose unacceptable risk to the patient or raise concern that the patient would
   not comply with protocol procedures

   - Subjects may co-enroll on other investigational studies except for investigational
   studies whose primary aim is the prevention of GVHD

   - No additional restrictions exist regarding co-morbid disease or incurrent illness

   - Patients will be excluded from the trial if they have had a history of allergies or
   intolerance to fructooligosaccharides or the components of FOS including fructose and
   glucose

   - No exclusion is necessary based on the use of other concomitant medications;
   specifically there is no prohibition of concomitant antibiotic, antiviral or
   antifungal therapy; subjects may co-enroll on other investigational studies except for
   investigational studies whose primary aim is the prevention of GVHD

   - Pregnant or nursing patients will not be included in the study