Mode of the expression of phosphofructokinase (PFK) -M and -L genes was examined in various human tissues including muscle, placenta, liver, kidney, pancreas, stomach and reticulocytes. The gross level of mRNA expression of PFK-M and -L genes was estimated by Northern analysis. Polymerase chain reaction was used to detect mRNA expressed at low levels in these tissues. Tissue-specific expression of alternatively spliced PFK-M gene transcripts was also determined by polymerase chain reaction. The results indicated that alternative splicing of PFK-M gene transcripts was controlled in a tissue-specific manner.