Spermatogenesis is a dramatic differentiation process which involves very selective but poorly characterized gene-expression patterns. To gain insight into this process, we have investigated the expression during spermatogenesis of the genes that encode phosphoglycerate mutase, an essential glycolytic enzyme for the spermatozoa energy supply. By using cDNA and genomic probes we demonstrate the presence in testis of a mRNA corresponding to the muscle-specific phosphoglycerate mutase which shows a longer poly(A) tail. This muscle-specific gene is submitted to developmental regulation during testis maturation and begins to be expressed at postnatal day 22, when germ cells start to enter into meiosis. Northern blot and in situ hybridization experiments show that in contrast to what happens during skeletal-muscle differentiation, PGAM-M gene expression during spermatogenesis is not coupled to constitutive phosphoglycerate mutase (PGAM-B) gene repression. Thus, the muscle-specific PGAM-M gene constitutes a meiotic gene and therefore represents a very interesting model to study differential tissue-specific gene expression.