Four Midwestern packing plants (designated as plants A, B, C, and D) were visited on 53 occasions, and tissue samples were collected postmortem from a total of 2,019 pigs to determine the frequency of the HAL-1843 mutation of the ryanodine receptor gene in dead (DOA), nonambulatory-noninjured (NANI), and normal animals. The mutation was present in all 3 classes of pig. There was a greater frequency of carriers in DOA animals than in the normal or NANI pigs. The 55 pigs that had at least 1 copy of the mutation came from 53 farms; therefore, the mutation was relatively widespread, being present in approximately 11% of the farms sampled. Therefore the data shows that the HAL-1843 mutation is still present in US commercial pig populations, it is low in frequency and therefore not a major cause of transport losses.