Genetic typing of alpha 1AT was performed in 3751 individuals from Italian towns. The following was observed: (a) The pathologic phenotypes (SZ, MZ, ZZ) appeared to decrease progressively from northern to southern Italy; (b) the distribution of the PiM suballeles showed considerable geographic variability, but the suballele M2 was more frequently encountered in southern Italy; and (c) in the large cities of southern Italy, the frequency of the deficiency more closely resembled that found in northern Italy than that of the remaining populations of the south.