Standard biplane chest X-rays were tested for the validity of morphometric criteria in the diagnosis of pulmonary artery hypertension. Twenty-seven patients suffering from chronic obstructive lung disease were examined and compared with a control group without cardiopulmonary disease. The diameter of the right and left pulmonary artery, pulmonary conus and the hilar-to-thoracic ratio were significantly increased in patients with chronic obstructive lung disease (p<0.0001). Measurement of the right pulmonary artery was 19.7+-3.9 mm compared to 13.6+-1.2 mm of the control group; mean hilar thoracic index was 0.35 compared to 0.31. Thus if the width of the descending branch of the right pulmonary artery was above 16 mm, pulmonary arterial hypertension was suggested, with a specificity of almost 100%, although the sensitivity of the diagnosis was only 59%. The mean pulmonary arterial pressure obtained by right heart catheterization correlated poorly with the morphometric criteria obtained. (orig.).