Regional distribution of pulmonary ventilation and perfusion has been determined of 13 patients with chronic obstructive pulmonary disease (COPD). Eight patients had alpha 1-antitrypsin deficiency (alpha 1 ATD). Ventilation studies were carried out using xenon-133 (133Xe) and krypton-81m (81mKr) gases. Trapping indices were determined from the wash-out part of the xenon ventilation studies. Results obtained from patients were compared with those of normal controls. Ventilation studies with 81mKr showed pulmonary changes more clearly than did 133Xe studies and the trapping of radio-xenon was more extensive in lung bases than in apices whether or not the patients had alpha 1 ATD. The distribution of perfusion followed a pattern similar to that of ventilation, but did not differ statistically from that of the normal controls.