The aim of this study was to define the presence, histological types and extent of bronchiolitis obliterans (BO) after lung transplantation and to discuss the place of bronchiolitis obliterans in the progressive obstructive ventilatory disorder observed in some patients and considered to correspond to "chronic lung rejection". The histological lesions were studied in 16 subjects surviving for more than one month after lung transplantation or heart-lung transplantation: 12 autopsies, 3 surgical biopsies and one lung explanted for retransplantation. Thirteen subjects presented lesions of bronchiolitis obliterans: 5 cases of granulomatous BO, 6 cases of proliferative BO, one acute necrotising BO and one tuberculous granulomatous BO. Three of these patients presented an obstructive ventilatory disorder: one death on the 213rd day (acute necrotising BO), one retransplantation on the 672nd day (granulomatous BO), one death 53 days after surgical biopsy on the 247th day (proliferative BO). Two patients undergoing surgical biopsies with lesions of proliferative BO are still alive (cases 15 and 16) and do not present any signs of obstructive ventilatory disorder. This study suggests the existence of various histological types of BO in transplanted lungs, which is not exclusively of immunopathological origin, that infections and various inhalations also play a role and that alterations of pulmonary structures other than bronchioles are also involved in the pathogenesis of the obstructive ventilatory disorder (functional destruction of the transplant), corresponding to "chronic lung rejection".