Most electrophoretic variants of alAT are associated with normal serum levels of this protease inhibitor. However, several variants are associated with either a partial deficiency or total absence of the protease inhibitor in sera (5). Inheritance of specific combinations of these variant alleles can result in severe alAT deficiency, which predisposes affected individuals toward the development of pulmonary emphysema. The two most frequent variants associated with a deficiency of the circulating level of alAT are designated PiS and PiZ, which exhibit allelic frequencies of 0.02 to 0.03 and 0.01 to 0.02, respectively (3, 6). Additional rare alAT alleles associated with either a partial deficiency (7-9) or total absence of serum o. Al'(10-13) have also been identified.