Gene frequencies of PGM1 phenotypes as obtained by isoelectric focusing on polyacrylamide gel in the pH range from 4 to 8 were determined in 501 samples of Swiss blood donors. Results were in good agreement with the expected distribution according to the Hardy-Weinberg law. Frequencies were PGM1a1 = 0.6278, PGM1a2 = 0.1936, PGM1a3 = 0.1297, PGM1a4 = 0.0489. Comparison with other data of the white population showed no significant differences. Isoelectric points of regular and rare gene products were determined. Application of the method in routine paternity testing is discussed.