Several reports suggest a relationship between bone marrow transplantation and pancreatic damage. The authors describe two patients with pancreatic insufficiency after bone marrow transplantation. The first patient had weight loss arising from steatorrhea secondary to severe pancreatic insufficiency (lipase output result <3% of normal) due to pancreatic atrophy. The second patient had steatorrhea secondary to intestinal bacterial overgrowth, but moderate pancreatic insufficiency was present (results of trypsin and lipase outputs were 50 and 30% of normal). Before the diagnosis of pancreatic insufficiency, both patients had acute graft vs host disease and the second patient had chronic graft vs host disease. We conclude that graft vs host disease after bone marrow transplantation may damage the pancreas. Patients with persistent malabsorption after bone marrow transplantation should be tested for exocrine pancreatic insufficiency.