The expression of the F-type 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase mRNA was studied during liver regeneration by three independent assays: Northern blot analysis, reverse transcription-polymerase chain reaction and ribonuclease protection. We demonstrate the presence of F-type mRNA in foetal and adult rat livers and a transient increase in its levels with a maximum at 12 h after partial liver resection. The time course of F-type mRNA induction differs from that reported for the L-type isoform, suggesting differences in the regulation of the expression of F- and L-type isoforms of the bifunctional enzyme during liver regeneration.