Histopathological findings in the lungs in a series of autopsies on 87 patients suffering from various types of leukaemia or lymphoma who had received no treatment, or various combinations of radiotherapy, chemotherapy and bone marrow transplantation were reviewed. Thirteen untreated patients showed neoplastic infiltration (4), thromboembolism (4), infection (5) or amyloidosis (1). Seventy-two treated cases showed malignant infiltration (14), vascular damage (21), infections (32) and/or diffuse alveolar damage (47). One patient treated with local irradiation for myeloma had acute bronchopneumonia alone and another treated with [32P] for polycythaemia rubra vera had extensive thrombo-embolism of the large pulmonary vessels. Clinical and autopsy evidence of infection correlated very poorly. Non-infective pulmonary disease was a frequent finding. Bacterial, fungal or pneumocystis pneumonia particularly affected the chemotherapy and radiotherapy groups, while cytomegalovirus infection was seen only in the bone marrow transplant group. This study shows that diffuse alveolar damage is a common and important problem in patients treated with radiotherapy and chemotherapy.