This report describes the use of octreotide, a synthetic somatostatin analogue, for severe diarrhea caused by acute intestinal graft-versus-host disease (GVHD) after bone marrow transplantation. A 22-month-old boy suffered grade 4 intestinal GVHD, with profuse diarrhea, intestinal inflammation, and grossly bloody stools after matched, unrelated donor transplant for biphenotypic leukemia. He required intensive blood product support. In addition to aggressive anti-GVHD therapy, octreotide acetate was initiated at 30 microg (2 microg/kg) intravenously 3 times per day and escalated to continuous infusion at 15 microg/hr (1 microg/kg per hour). The diarrhea did not improve with anti-GVHD treatment. However, moderate dose octreotide therapy resulted in prompt control of the bloody diarrhea, which rebounded on cessation of octreotide therapy. Rebound diarrhea responded promptly when the dose of octreotide was escalated. Octreotide was associated with an exacerbation of preexisting hypertension, but it appeared to be effective for control of severe, bloody diarrhea caused by acute GVHD in a child, with manageable side effects. Further studies of this application in infants and children are warranted.