The distribution of phenotypes of alpha 1-antitrypsin (Pi) in 909 unrelated Danes was determined by the use of separator isoelectric focusing in agarose gel. The frequencies calculated were: PiM1 = 0.728, PiM2 = 0.136, PiM3 = 0.082, PiZ = 0.023, PiS = 0.022, PiF = 0.006, Pivar = 0.003. The segregation of phenotypes in 39 families with 94 children is presented. The advantages and disadvantages of the method are discussed.