I. To determine if hematopoietic stem cell transplant (HSCT) patients treated with a probiotic (Lactobacillus GG [Lactobacillus rhamnosus GG])-containing diet compared to those not assigned to receive probiotic have a lower incidence of grade 1 upper gastrointestinal (GI) or grade 2-4 lower GI acute graft-versus-host disease (GVHD) (aGVHD) using Center for International Blood and Marrow Transplant Research (CIBMTR) scoring than those not prescribed a probiotic.