Twelve consecutive patients with systemic lupus erythematosus (SLE) and chest symptoms of at least 3 months' duration were investigated with spirometry, lung mechanics at rest and exercise, diffusion capacity and right heart catheterization. Vital capacity (88% of predicted, p less than 0.05), and FEV1 (84%, p less than 0.01) were decreased in the study group, but spirometric and diffusion capacity abnormalities were moderate compared with previous studies. The single breath CO2 test showed, in six patients, ventilation-perfusion mismatch with patterns typical for either bronchial obstruction or vascular disease. Non-respiratory factors were responsible for reduction of working capacity (on average 68% of predicted normal values (p less than 0.001]. Two patients with pulmonary hypertension were identified by right heart catheterization. One of them had overlap features with the CREST syndrome. Both these patients had abnormal SBT-CO2 test and diffusion capacity, along with diffuse perfusion defects on perfusion scintigraphy. The low frequency of pulmonary function abnormalities in this study suggests that irreversible pulmonary damage is uncommon in SLE.