The distribution of the phenotypes of alpha-1-antitrypsin (Pi) was investigated in a Swiss population sample of 1,148 unrelated individuals using isoelectric focusing with a immobilized pH gradient. A short focusing period of only 2 h using high-voltage is an additional asset of this modified method. All common as well as the rarer phenotypes were reliably detected. However, detection of Pi M4 required a narrower pH range as chosen for routine work. The allele frequencies found were: PiM1:0.7121; PiM2:0.1381; PiM3:0.0976; PiS:0.0383; PiZ:0.0113; PiVar(I, N, V.Vdon):0.0026.