The alpha1-antitrypsin phenotypes of two Dutch population groups (consisting of 672 and 802 individuals) were determined by the isoelectric focusing technique, which due to its recent development, has been used for the first time in large-scale phenotyping. As in other population studies on the alpha1-antitrypsin phenotype distribution, Pi M is the most frequently occurring allele. The two investigated groups exhibit remarkable differences, both to other studied groups as well as to each other. The most interesting results are probably the high frequencies of the alleles Pi- and of the recently discovered Pi MN. Comparison with phenotype studies carried out in other populations is also presented.