Pulmonary hemodynamics have been extensively investigated in patients with chronic bronchitis or in ‘mixed’ patients (chronic bronchitis + emphysema) but rarely in patients with markedly predominant emphysema. We have investigated a large series (n = 151) of such patients, emphysema having been assessed on radiological, clinical and functional grounds. The mean age was 58 ± 10 years; vital capacity (VC, % of predicted) = 81 ± 19; forced expiratory volume in 1 s (FEV1)= 1,198 ± 589 ml; FEV₁/VC = 38 ± 12%; PaO₂ = 72 ± 11 mm Hg; PaCO₂ = 37,5 mm Hg. Pulmonary hypertension (PH), defined by a resting pulmonary artery pressure (PAP) of ≥20 mm Hg, was present in only 31 of 151 patients. During steady-state exercise (40 W or less) an abnormally high PAP (≥30 mm Hg) was observed in 99 of 151 patients. Resting and exercising PAP were poorly correlated with resting PaO₂ and PaCO₂, but were better correlated with the amplitude of the respiratory pressure swings, FEV₁, the transfer factor and exercising PaO₂. Patients with PH (n = 31) showed significantly more obstruction and pulmonary distension than the remainder, but they did not differ from the non-PH patients with regard to resting PaO₂. It is concluded that: (1) resting PH is not the rule in diffuse emphysema but exercising hypertension is frequent (2 of 3 patients), and (2) hypoxemia is not a determining factor of hemodynamic abnormalities in emphysema