The purpose of this study is to examine the relationships among severity of illness, quality of life and functional ability; and to determine the impact of oxygen therapy on functional ability in patients with Alpha l- Antitrypsin Deficiency. Adult Alpha l-Antitrypsin deficient patients, admitted for evaluation of their lung disease, respond to a questionnaire that measures four aspects of quality of life: emotional function, fatigue, mastery, and dyspnea. Patients walk for 6 minutes with oxygen via nasal cannula or with placebo. Measurements include the distance walked, the oxygenation and pulse rate during the walk, and the dyspnea intensity at the end of each walk. To date we have collected date on 32 subjects. Preliminary analysis indicates no advantage of oxygen over placebo in terms of functional outcomes. An amendment to this protocol was approved to test patients with more advanced disease status using oxygen as compared to paced breathing, and 10 subjects have been accrued thus far for this amendment. Data analysis is pending.