The aim of the study was to compare the shares of MHC isoforms in the muscle tissue of bulls differing in terms of breed and age using SDS-PAGE. The share was analysed as a factor which could have modified tenderness and water holding capacity of meat. Investigations were conducted on 73 young bulls of the Black-and-White, Polish Red, Hereford and Limousine breeds, slaughtered at the age of 6, 9 and 12 months, generally with 5 animals in each age group. The composition of MHC isoforms (type 2a, 2x and I) in the muscle tissue of the analysed cattle was related to the instrumental tenderness evaluation, as well as water holding capacity of meat on the basis of drip loss at 48, 96 and 240 h after slaughter. It was shown that better tenderness and water holding capacity of meat from Hereford bulls aged 12 months were accompanied by an increased share of MHC isoform type 2a, corresponding to fast-twitch, intermediate, oxygen glycolytic fibers.