PiM subtypes were determined by isoelectric focusing of the sera of 746 Japanese at the age of 16-60 years. The gene frequencies were calculated: PiM1 = 0.7855, PiM2 = 0.1528 and PiM3 = 0.0617. The serum concentration of alpha-1-antitrypsin was measured by laser-nephelometric immunoassay of the sera of 284 individuals. A statistically significant difference (p less than 0.01) in the serum concentration was found between M1 (2.63 +/- 0.67 g/l) and M1M2 (2.39 +/- 0.59 g/l).