Slow progression of emphysema and lack of an adequate control group have made it difficult to evaluate the proteinase inhibitor through a controlled clinical trial. A patient registry was an alternative method to collect data on the effect of long-term replacement therapy with A1Pi on rate of decline of lung function. The registry also included individuals who did not receive the replacement therapy in order to obtain a better knowledge of the rate of decline of lung function associated with the congenital deficiency for alpha1-antitrypsin.