II. To determine if HSCT patients treated with a probiotic-containing diet compared to those not assigned to receive a probiotic have a: a) lower rate of organ-specific acute aGVHD (intestinal tract, skin, liver); b) lower rate of moderate or severe chronic GVHD (National Institutes of Health [NIH] consensus scoring) at 6 months and 1 year post transplant; c) shorter duration of immunosuppressive therapy (normalized for age and degree of human leukocyte antigen [HLA] match); d) lower rate of bacterial and/or opportunistic infection.