 4. Patients who have had persistent GI GVHD manifested by diarrhea with stool volume 500 mLday in the absence of nausea or vomiting may be deemed as having Grade B GVHD if other causes of diarrhea have been ruled out e.g., C. difficile or cytomegalovirus CMV infection, oral magnesium administration and if the low stool volume reflects the effects of fasting or administration of narcotics or antidiarrheal medications. 