A simple PCR-based allele detection system has been developed to assist in the management of the two most prevalent double-muscled (mh) breeds in the U.S. Application of this assay will permit the implementation of structured mating systems dependent on precise genotypes at the mh locus. The genetic assay uses standard fluorescent genotyping technology and relies on the unique nucleotide composition of wild-type and mutant alleles of myostatin, the gene underlying the double-muscled phenotype. We present data demonstrating the efficacy of this fluorescent primer-based PCR assay in genotyping animal populations carrying normal and(or) mutant alleles of the myostatin gene.