In cattle, expression of the IIb myosin heavy chain (MyHC) isoform has been demonstrated only in extra-ocular muscles. In this Study, we demonstrated for the first time its expression in the Semitendinosus and Longissimus thoracis muscles of a French beef breed, Blonde d'Aquitaine. Several techniques were used: RT-PCR, electrophoresis, western blotting, histochemistry with ATPase staining and immunohistochemistry using a combination of anti MyHC antibodies on serial sections. We found that MyHC Ilb was expressed at the mRNA level in the two muscles of the cattle studied. However, the protein was observed at the tissue and cellular levels in only five of the 22 young bulls analysed, suggesting complex regulation of its expression. Using immunohistochemistry we demonstrated the presence of this MyHC isoform in pure fibres and also in hybrid fibres in co-expression with other MyHC.