The lower lobe of the left lung was transplanted from a mother to her child, who previously had received a bone marrow transplant from the mother because of an immune defect. After the bone marrow transplant the child had developed progressive pulmonary fibrosis (obliterative bronchiolitis). The surgical procedure and the early postoperative period has been uncomplicated. Immunosuppression with corticosteroids was only given for a short period, after which no immunosuppressive treatment has been given. The operation and results for both donor and recipient are described. The early results are promising, but rehabilitation is progressing slowly.