Pulmonary disease is recognized to occur as a complication of Sjögren's syndrome and we have studied 17 patients, the majority middle-aged women, with this association. Eight had sicca syndrome alone and nine had Sjören's syndrome in association with a connective tissue disease. Various pulmonary disorders were found: 10 had diseases mainly affecting pulmonary parenchyma (recurrent pneumonia, granulomatous infiltration, pseudolymphoma and fibrosing alveolitis) and six had disorders of the airways (bronchitis, bronchiectasis and asthma). One patient presented with a mediastinal immunoblastic lymphoma. To test the hypothesis that physical factors such as the retention of viscid mucus may play a part in the development of lung disease in Sjögren's syndrome, we have measured mucociliary clearance in patients with Sjögren's syndrome using 99Tc-labelled polystyrene particles. The mucociliary clearance rate was found to be normal from central airways and the whole lung clearance rate was significantly increased in Sjögren's syndrome compared with normal controls. The latter was attributed to the failure of penetrance of the radioaerosol into the periphery of the lung consistent with obstruction of small airways in Sjögren's syndrome. The patients with Sjögen's syndrome and lung disease were characterized by a number of immunological markers irrespective of the presence or type of associated connective tissue disorder. The commonest found were speckled antinuclear antibody by indirect immunofluorescence, antibodies to the acidic nuclear antigen B by counterimmunoelectrophoresis, increased serum DNA binding, increased levels of circulating immunoglubulins, rheumatoid factor in high titre and circulating soluble immune complexes as detected by Clq binding assay.