We performed phenotyping of human phosphoglucomutase 3 (PGM3) and screening for mutations in the human N-acetylglucosamine-phosphate mutase gene (AGM1) to identify PGM3 as AGM1. By sequencing the coding region of AGM1, two alleles containing a G or A base at nucleotide 1396, that can respectively encode aspartic acid or asparagine at codon 466, were identified. Cell extracts of COS7 cells after transfection with the pcDNA 3·1(+) plasmid containing an AGM1 allele with 1396G or 1396A showed similar electrophoretic patterns to the PGM3 1 or PGM3 2 protein, respectively, with the isozyme detection method used for PGM3 phenotyping. The genotypes determined by the two alleles of AGM1 coincided exactly with the PGM3 phenotypes in 20 individuals. We also investigated the allele frequency of the AGM1 nucleotide polymorphism in a Japanese population by DNA sequencing and found that the frequencies of alleles 1396G and 1396A were similar to previously reported PGM3*1 and PGM3*2 frequencies. Overall, the facts that the AGM1 gene product shows PGM activity, AGM1 is polymorphic, the electrophoretic mobility is similar between AGM1 allele-specific products and PGM3 1 and 2 proteins, PGM3 phenotypes and AGM1 genotypes completely coincide in 20 individuals, and AGM1 allele frequencies are similar to those of PGM3*1 and PGM3*2 in Japanese populations, suggest that PGM3 is identical to AGM1.