Significant abnormalities in pulmonary function are encountered in about 24% of patients with primary Sjögren's syndrome. The most common cause of dyspnoea is interstitial fibrosis, with a prevalence of around 8%, but a number of other pathologies may be encountered in the lungs of these patients (Table 1). Lymphoproliferative disorders are relatively uncommon, but these apparently benign lesions may harbour malignant potential. Interstitial fibrosis and the lymphoproliferative disorders may be responsive to corticosteroids or cytotoxic agents, and it is therefore important to establish an accurate diagnosis at an early stage. On the basis of our experience we would recommend the investigative strategy outlined below. Patients should be screened for significant lung disease by taking a careful history of respiratory symptoms followed by standard pulmonary function testing (including measurement of carbon monoxide diffusing capacity) and chest radiography. High resolution computed tomography is a non-invasive technique that should prove superior to chest radiography in the detection of early cases of interstitial fibrosis. When the disease is patchy it may be useful in identifying areas of maximal involvement for subsequent biopsy. Bronchoalveolar lavage is a sensitive tool in the non-smoker, but lacks the specificity to command a significant role in the investigation of pulmonary pathology in these patients. One exception to this may be in the investigation of the clonality of lymphocytes which may allow early and specific diagnosis of lymphomatous proliferation. The application of techniques such as the polymerase chain reaction may assist in the investigation of the role of the Epstein-Barr virus in the causation of lymphoproliferative lesions. In most patients with significant symptoms and abnormalities of pulmonary function a tissue diagnosis will be required, either by transbronchial biopsy or by open lung biopsy. Both bronchial and interstitial lung tissue should be obtained where possible. Histological confirmation is probably mandatory when there is a recent history of parotid enlargement, weight loss or the appearance of a monoclonal gammopathy. Advances in our understanding of the mechanisms of the MALT system may provide the key to unlocking some of the mysteries of 'autoimmune' diseases such as Sjögren's syndrome. The response of lymphoproliferative disorders to immunosuppressive therapy provides hope that if the diagnosis of sicca syndrome can be made earlier lymphocyte induced tissue damage may be halted or reversed.