Adoptive transfer of allergen-specific immunoglobulin E (IgE) from atopic donors to nonatopic recipients occurs during the first year following bone marrow transplantation (BMT). Mature B- and T-cell clones with allergen-specific memory and hematopoietic progenitor cells are transferred through BMT. The objective of this study was to characterize the long-term rate of allergic sensitization and development of clinical allergic diseases following BMT from atopic donors. A long-term follow-up study was conducted in a cohort of donor and recipient pairs with moderate-to-severe allergic disease in the donor prior to BMT. Assessments of allergen-specific IgE, clinical rhinitis, and asthma were made in the donors prior to BMT and in the recipients with a mean follow-up of 15.5 years after BMT. From an initial cohort of 12 bone marrow transplant recipients who received marrow from allergic donors, 5 long-term survivors were identified. Allergen-specific IgE transferred from donor to recipient following BMT frequently persisted, and a high rate of de novo allergic sensitization was observed between 1 and 14 years after BMT. These events were associated with elevation in total IgE, and development of allergic rhinitis and asthma at long-term follow-up. We conclude that marrow-derived immune cells from allergic donors can transfer the predisposition to allergy and asthma.