Phosphofructokinase (PFK) is a key rate-limiting enzyme in glycolysis and represents a major control point in the metabolism of glucose. There are at least three known isoforms of PFK in humans, referred to as the muscle, platelet, and liver forms, each of which is differentially expressed in various tissues. The gene for muscle phosphofructokinase, PFKM, is mutated in Tarui disease and conceivably contributes to non-insulin-dependent diabetes mellitus (NIDDM). Based on physical and genetic mapping, we have found that the gene for PFKM does not map to chromosome 1 as previously described, but instead maps to chromosome 12. PCR analysis with a somatic cell hybrid mapping panel using primers derived from intron 6 and exon 18 of the PFKM gene showed consistent amplification of cell lines containing chromosome 12 (concordance, 100%). Fluorescence in situ hybridization analysis with CEPH YAC 762G4, isolated with exon 18 primers, indicated that this clone maps to 12q13, centromeric to the diacylglycerol kinase gene (DAGK) at 12q13. 3. A highly informative genetic marker isolated from YAC 762G4 was used to map PFKM genetically between the CHLC framework markers D12S1090 and D12S390. This placement for 762G4 was significantly proximal to the recently reported locus for a third gene for maturity onset diabetes of the young (MODY). The PFKM-associated microsatellite will be a valuable tool in the evaluation of PFKM in diabetic populations as well as in linkage analysis in families with Tarui disease.