Lysates of erythrocytes, leukocytes, lymphocytes, and extracts of sperms were investigated for the PGM1 isozymes by three techniques: starch gel electrophoresis, high voltage thin-layer agarose gel electrophresis, and thin-layer isoelectric focusing on polyacrylamide gel. On starch, only the well known common phenotypes 1, 2-1, and 2 were demonstrable. On agarose, different distances of the two main cathodal bands (a,b) among the phenotypes 2-1 were noted. Furthermore, on agarose, some types considered as homozygous on starch gel had a single, sharp banded pattern while others were broad and blurred. Optimal separation was achieved by isoelectric focusing on polyacrylamide gel. In 291 leukolysates, 10 different phenotypes were identified. These are considered as gene products of 4 different common allesles at the PGM1 locus as suggested by preliminary family investigations. In a random population from Hessen these four alleles had the following frequencies: PGM1al 0.6186, PGMa21 0.1718, PGMa31 0.1426, and PGMa41 0.067, The preliminary designation a1, a2, a3 and a4 was chosen as the assumed polymorphism was demonstrated on acrylamide and agarose. The sum of the frequencies PGMa11 and PGMa31 (the gene products of which have apparently the same electrophoretic mobility on starch) is similar to the frequency of the old PGM11 allele (0.757) in Caucasoids, PGMa21 and PGMa41 have a frequency of 0.2388 corresponding with the frequency of the old allele PGM21.