Research suggests that the microbiota may be a predictor of mortality in allogeneic hematopoietic-cell transplantation. Studies are investigating the relationship between the microbiome and transplant outcomes, including the risk of relapse and complications such as graft-versus-host disease. The microbiota's potential as a therapeutic target is also being explored, with possible interventions including fecal microbiota transplantation and modulation of the gut microbiome.