A double tube allele specific PCR assay was developed for a rapid and accurate detection of the porcine Ryanodine receptor genotypes using the allele specific pimer PCR. The assay, a modification of Zinovieva` single tube allele specific(STAS) PCR, reduced significantly primer dieter artificial band and determined allelic variations in simple, accurate and cost-effective ways. PCR primers were designed as followed ; two allele-specific `internal` primers[Int 1 for the normal allele N 5`-AGTAATGAGATCTTGGTTGGA(G→T)CG-3`, Int 2 for the mutant allele n : 5`-GTGCAATGGTGTGGCCG (T→C)GT-3`] were recognized with their 3`nucleotide the allelic variation. In order to increase the allele specific annealing an additional mismatch at position 3 from the 3` end of each primer was introduced. The common `external` primers(Ext 1, Ext 2) were located at different distances from the point mutation(nt 1843, C→T), so that different fragment lengths were generated for each allele. In the case of the gene, in normal(NN) and mutant (nn) homozygotes, only one fragment of 533 by or 823 bp, respectively, was amplified, whereas in heterozygotes (Nn) both fragments were detected. Independently from the genotype, an additional product(1312 bp) of the common `external` primers was amplified in. the single tube method. The use of the allele specific PCR for detecting allelic nucleotide exchanges offers some obvious advantages the presence of restriction endonuclease sites is not required and the allelic variations are visualized by simple agarose gel electrophoresis. As compared with the PCR-RFLP this modified method is simple, reliable and time and cost effective and thus can be applied in large scale to establish the program for testing and removal of the genes associated with the breeding of swine.