A restriction endonuclease assay (REA) that reveals a C/T transition in the ryanodine receptor gene (ryr-1 locus) was proposed to test swine for malignant hyperthermia. The REA was tested in a heterologous pig population of 1,227 individuals representing Hampshire, Duroc, Landrace, and Yorkshire breeds. Of this group, 713 pigs had been classified on the basis of the halothane challenge and progeny testing into the three possible Hal genotypes (685 negatives, 24 carriers, and 4 susceptibles). The REA confirmed the four susceptibles as T/T, 17/24 carriers as C/T, and 659/685 negatives as C/C. The rest of the sample was constituted of 514 pigs that had not been selected on the basis of the halothane gene. The proportions of C/T and T/T pigs within the breeds represented were 3.2 and 1.6% for Duroc, 27.3 and 1.4% for Landrace, and 17.9 and 1.9% for Yorkshire. No T/T allelic pairs were found in the Hampshire breed, although the sample was very small. Genotypic distribution and allelic frequencies at the ryr-1, Phi, and Pgd loci were reported among the breeds.