Persons with alpha1-antitrypsin (A1AT) deficiency and chronic obstructive pulmonary disease (COPD) have been tested for the clinical value of regular intravenous infusion with A1AT in two small double-blind randomised controlled trials. The trials found a statistical significant reduction in the decrease of lung density measured by computed tomographies, but found no clinical nor statistical significant difference in respiratory symptoms, quality of life, lung function, use of medication, exacerbations, respiratory infections or survival. Based on the present evidence A1AT substitution therapy cannot be recommended.