2-D electrophoresis was used to investigate the effects of a quantitative trait locus for muscle hypertrophy on sarcoplasmic protein expression in ovine muscles. In the Belgian Texel breed, the QTL for muscle hypertrophy is localized in the chromosomal region of the myostatin-encoding gene. Based on microsatellite markers flanking the myostatin gene, we compared the hypertrophied genotype with the normal genotype. The average age of animals was three months. Among the four muscles studied, in hypertrophied genotype only the vastus medialis was normal, whereas the others - semimembranosus, tensor fasciae latae and longissimus dorsi - were hypertrophied. In the hypertrophied genotype, these muscles showed up-regulation of enzymes involved in glycolytic metabolisms together with oxidative metabolism in longissimus dorsi muscle. Certain chaperone proteins including glutathione S-transferase- Pi, heat shock protein-27, and heat shock cognate-70 were also more highly expressed, probably due to increased use of energetic pathways. Expression of the iron transport protein transferrin was increased. Alpha-1-antitrypsin was the only protein showing a similar pattern of expression (i.e. less expressed) in all four muscles of the hypertrophied genotype. It is suggested that transferrin and alpha-1-antitrypsin may interact to reinforce myogenic proliferative signalling.