Chronic organ dysfunction of the lung allograft is the most common cause of death in lung transplant recipients after the first postoperative year and is a major cause of morbidity in the long-term care. It affects every second recipient surviving 5 years after transplantation (Boehler, Estenne 2003). Obliterative bronchiolitis (OB) is the histo-pathological process underlying chronic organ dysfunction after LTx. Bronchiolitis obliterans syndrome (BOS) is the clinical definition of chronic organ dysfunction following lung transplantation (LTx) and refers to a progressive obstructive ventilatory disorder. Staging is performed according to baseline values of forced expiratory volume after LTx (Estenne et al. 2001).