Alpha 1-antitrypsin (alpha 1-AT) deficiency is very rare in Japan although it is one of the most common hereditary disorders in Caucasians. Only 12 cases of alpha 1-AT deficiency have been reported in Japan. Their genetic abnormalities have already elucidated in 10 cases: Mnichinan, a heterozyge of Mmalton, 7 unrelated cases of Siiyama, and a case of 14q-syndrome. The Siiyama is the first prevalent deficient variant in the race other than the Caucasian race. The Siiyama mutation occurred on the normal alpha 1-AT variant M1 (Val213) which seems to be evolutionally newer than M1 (Ala213) on which the Z type mutation occurred. The result that alanine residue was not detected at 213 amino acid position in alpha 1-AT genes of 193 Japanese volunteers may be the reason why genetically proved Z deficient variant have not been reported yet in Japan.