Purpose: To assess serial CT as a measure of the progress of emphysema in patients with severe α₁-antitrypsin deficiency (phenotype PiZ). Material and Methods: In a randomized placebo-controlled study of α₁-antitrypsin augmentation therapy, 22 patients with moderate emphysema were followed for 2-4 years with an annual lung CT. The images were analysed by means of semiautomatic lung detection, and the degree of emphysema was quantitated by the density-mask and the percentile methods. The influence of lung volume was standardised by a regression model. Results: A highly significant decline in Hounsfield units (HU) was found in low-density areas corresponding to a mean (SE) annual loss of lung tissue of 2.1 (0.4) g/l lung volume. Analysis of a single slice at 5 cm below the level of the carina gave comparable results: 2.4 (0.4) g/1. Conclusion: Serial CT is a sensitive measure of the progress of emphysema in patients with severe α₁-antitrypsin deficiency.