Localization of all subunits of cAMP dependent protein kinase (PKA) mRNAs and their changes of expression after denervation were examined in rat tongue skelet al muscle by in situ hybridization histochemistry. Among all PKA subunits only RIα subunit mRNA was detected in the skelet al muscle, whereas positive signal of all subunits mRNA were observed in some haematocytes or lymphocytes within the tongue tissue. The RIα mRNA was distributed in a restricted area near the endplate. The mRNA level was substantially induced by the hypoglossal nerve transection, suggesting that the up-regulation of RIα mRNA leading to the down-regulation of PKA activity may contribute to some intracellular signalling modulation or to muscle specific gene transcription after the denervation.