Purpose: To assess serial CT as a measure of the progress of emphysema in patients with severe α1,-antitrpsin 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/l. Conclusion: Serial CT is a sensitive measure of the progress of emphysema in patients with severe α1-antitrypsin deficiency.