Effects of 12 months steroid treatment on pulmonary haemodynamics in 24 patients with pulmonary sarcoidosis, stage II and III, were investigated. All patients had a chest radiograph, lung function tests, and pulmonary haemodynamics (measured at rest and during submaximal exercise) prior to the treatment. Resting pulmonary hypertension was found in 3 patients. In 18 an abnormal increase in pulmonary arterial mean pressure (PAP) on exercise was observed. All investigations were repeated after a year of treatment. In almost all patients (22) a regression of radiological changes in the lungs and improvement of pulmonary function were observed. The changes in pulmonary circulation were less uniform. In only half of the patients studied was regression of the disease seen on chest X-ray and improvement in lung function accompanied by improvement in pulmonary haemodynamics.