We have identified novel transcriptional isoforms of the human and mouse genes encoding muscle type phosphofructokinase-1 (PFK-M). These isoforms are expressed specifically in the testis and in the mid-gestation embryo, and have been termed TE-PFK-M (testis- and embryo-specific PFK-M). The 5'UTR of TE-PFK-M is composed of three newly identified exons that lie much farther upstream of the PFK-M coding region than the previously characterized 5'UTR. In addition, this upstream region encodes a series of small polyadenylated transcripts, some of which share the same exons found in the 5'UTR of TE-PFK-M, and which may play some role in regulating TE-PFK-M expression. These findings indicate an even more complex level of control of PFK-M expression than previously thought. Published by Elsevier Inc.