Insufficient immunological reconstitution is one of the serious complications of allogeneic stem cell transplantation (SCT). We report a case of severely impaired B-lymphopoiesis after allogeneic SCT for CML. The patient's bone marrow and blood cells display complete chimerism and he is currently free from leukemia. His serum immunoglobulin levels are below detection level, and B cells are absent at 2 years post transplant in both the bone marrow and blood. Other populations appear to be normal. To the best of our knowledge, this is the first report of B-lymphopoiesis being undetectable more than 2 years after allogeneic SCT.