The complete mRNA sequence of the human liver-type phosphofructokinase (hPFKL) was determined. The sequence included 55 nucleotides of 5′ and 515 of 3′ noncoding regions, as well as 2,337 nucleotides encoding the 779 amino acids of the hPFKL. Extensive similarity (∼90%) in the coding region was observed between the hPFKL and the mouse PFKL, whereas the degree of similarity between different types of PFK, i.e., hPFKL and human muscle-type PFK (hPFKM), was merely 68%. Nevertheless, striking similarity between these different types of PFK was noticed when the amino acid residues creating the various active sites of the enzyme were compared. Human PFK L- and M-specific probes were constructed and used to quantitate the mRNA levels in fetal and adult brains and fetal liver. It was found that while the relative amount of PFKL mRNA in adult brain was one-fourth of that detected in fetal brain the level of PFKM mRNA in adult brain was slightly higher than in fetal tissue, suggesting that PFK expression might be controlled at the transcriptional level.