Subtypes of the protease inhibitor (Pi) alpha 1-antitrypsin were determined in sera from 752 unrelated individuals from Southern Germany. By isoelectric focusing nine common PiM subtypes were distinguished and several rare Pi variants were observed. Family studies confirm the existence of a fourth PiM suballele. The frequency of PiM4 was found to be 0.018. A survey of the distribution of Pi alleles is given; the application of Pi subtyping in cases of disputed paternity is discussed.