Graft-versus-host disease, a complication of allogeneic bone-marrow transplantation, involves primarily the skin, liver and intestines, but may also be associated with pneumonia. To determine the relation of graft-versus-host disease with pneumonia, we evaluated the autopsies of 59 allogeneic and two autologous recipients and 74 control patients with various pulmonary diseases, who had not received a bone-marrow transplant. Lymphocytic bronchitis, characterized by lymphocyte-associated necrosis of the bronchial mucosa and often the submucosal glands, was present in 12 of 20 patients with Grade 2 or greater graft-versus-host disease but in only three of 39 with Grade 0 to 1 disease (P less than 0.0005). Onset of respiratory disease correlated with the time of onset of graft-versus-host disease. Patients with lymphocytic bronchitis had a higher incidence of bronchopneumonia and acute bronchitis of the lower respiratory tract. Lymphocytic bronchitis did not occur in the controls and appears to be a component of graft-versus-host disease that leads to bronchopneumonia, probably through destruction of the mucociliary apparatus.