The arterial oxygen and carbon dioxide tensions (PO2 a and PCO2 a) and pHa were measured in 73 patients using capillary blood from a vasodilated ear lobe in the supine, sitting and standing positions. 46 patients had no known lung or heart disease and 27 patients had chronic obstructive airway disease (COAD). There was a significant age-related decrease in PO2 a. There were essentially no significant differences in PO2 a between the three positions in asymptomatic patients of different age-groups or in patients with COAD.