Hypoxic pulmonary vasoconstriction is considered as one of the factors leading to pulmonary hypertension in patients with chronic bronchitis, but the magnitude and the variability of the pulmonary vascular response to hypoxia in these patients have not been well established. We investigated the pulmonary hemodynamic changes induced by breathing two hypoxic mixtures (FIO2 = 0.15 and 0.13) in 26 patients with chronic bronchitis with airway obstruction (FEV1/VC = 49 +/- 14 percent). Results show that there is a wide variability of the pulmonary vascular response to acute hypoxia in chronic bronchitis patients, but it is not possible to say whether such differences play a role in the natural history of the disease.