Svanborg (1961) found normal pulmonary artery mean pressures in eleven patients with stage II sarcoidosis. By contrast Gluskowski et al. (1978) have shown few abnormally high values in the same condition. We have not found published haemodynamic data concerning stage O sarcoidosis. Thus we have performed right haemodynamic study (by Swan-Ganz catheters) on 19 patients with hystologically proven sarcoidosis (8 stage III, 6 stage II, 3 stage I and 2 stage 0). 13 of them underwent also haemodynamic study during exercise (1watt/Kg). Pulmonary artery hypertension (at rest or after exercise) was frequently found in stage III, and less frequently in stage II. In stage I pulmonary artery mean pressure was between 15 and 20 mmHg in three patients (out of three). In one case (out of two) in stage 0 (admitted to hospital owing to exertional dyspnoea) right heart catheterisation showed pulmonary hypertension during exercise in spite of normal pulmonary function tests (including spirometry, DLCO, pulmonary scintigrafic and X-ray pattern also using 3X magnification radiology).