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 greater than or equal to 20 mm Hg, was present in only 31 of 151 patients. During steady-state exercise (40 W or less) an abnormally high PAP (greater than or equal to 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.