Skeletal muscle fibre characteristics are key determinants of meat quality. High fibre diameters and shifting towards higher white fibre proportions lead to increasing R-values (degree of desamination of adenosine) and lactate-production, resulting in high incidences of pale, soft, exudative (PSE) meat and stress susceptibility in European and American pig breeds. Development of muscle fibres including their enzymes, is regulated by the MyoD-gene family together with transcription factors like FOS. We report on the associations between the chromosomal region of FOS with skeletal muscle fibre and metabolism traits. The BB genotype representing the European Pietrain breed had 10.9% more white fibres with fibre diameters decreased by 6.1%, with 3.9% higher R-values and 8.5% higher lactate levels than the AA genotype of the Chinese Meishan. Lactate levels and R-values per microm of fibre diameter were increased to 18.4 and 11.6% in the BB genotype. The contrast between the two quantitative trait loci (QTL) alleles associated with a polymorphism in the FOS gene explained up to 5.13% of the total variance. A new TaiI-restriction fragment length polymorphism (RFLP) connected to a Asn258/Ser mutation, located in a transcription activator region, was used to map FOS between markers S0115 and Sw581 on SSC7. The QTLs for skeletal muscle fibre and metabolism traits have been mapped to the marker interval around FOS. The present data suggest that variability in FOS gene may underlie phenotypic variation in skeletal muscle fibre and metabolism traits in the pig.