The experiment was performed on 33 young beef bulls of the following breeds: 16, Limousine (L), 9, Hereford (H), and 8, Charolaise, aged 7 to 14 months. The bulls were fed grass silage, maize silage and a concentrate, according to IZ-INRA standards (2001), assuming body weight gains of 1100-1200 g/d. At the end of the fattening period the bulls were slaughtered and samples of M. thoracis (MT) and M. semitendinosus (MS) were taken for fatty acid analysis. The intramuscular fat of MS, compared with MT, contained a significantly higher percentage of UFA, especially PUFA with 20 or 22 carbon atoms, and a lower concentration of SFA (P≤0.01). MS contained more n-6 and n-3 PUFA (P≤0.03), and was characterized by a slightly lower n-6/n-3 ratio (P= 0.07).