Twenty-one patients with chronic obstructive pulmonary disease were studied with right heart catheterization. The mean pulmonary artery pressure (PAP) was compared with several noninvasive tests. The pulmonary lobar diameter/thoracic ratio correlated with the PAP, r = 0.677, P less than 0.01. The oxygen saturation and pH were used to derive a calculated value for PAP. The calculated PAP correlated with PAP values measured below 40 mm Hg, r = 0.787, P less than 0.01 but correlated very poorly with PAP values measured above 40 mm Hg. The electrocardiogram revealed at least one criterion for right ventricular abnormality in all 18 patients with pulmonary hypertension, but was too nonspecific to correlate with PAP. The hemoglobin concentration did not correlate with PAP. There was such wide variation between the measured PAP and the various noninvasive tests that these noninvasive tests could not be used to accurately predict the PAP in an individual patient.