Several quantitative trait loci (QTL) affecting muscle glycogen content and related meat quality traits were mapped to pig chromosome 15 (SSC 15) by using a three-generation intercross between Berkshire x Yorkshire pigs. Based on the QTL location, the PRKAG3 (protein kinase AMPactivated, γ3 subunit) or the RN (Rendement Napole) gene, as it is popularly known, was considered to be a good candidate for the observed effects. Differences in the PRKAG3 gene sequences of the founder animals of the intercross were analyzed. The RN- mutation previously reported was not present in the cross but three missense substitutions (changes affecting proteins) were identified. To test the hypothesis that at least one of these mutations was associated with differences in meat quality, more than 1,800 animals from several unrelated commercial lines were genotyped for the candidate gene differences and an association study was performed. The results provide strong support for the presence of new economically important alleles (gene forms) of the PRKAG3 gene affecting the glycogen content in the muscle and the resulting meat quality. Because of their prevalence in the more common commercial breeds, the potential implications for the pig industry and consumers are probably more important than the original discovery of the RN- mutation.