An important problem in transplant medicine is the lack of organs and tissues for human transplantation. One of the promising areas of its solution today is the use of organs and tissues of animals — xenotransplantation. Pigs for medical and biological needs must be stress-resistant and adapted to the conditions of keeping and feeding within the vivarium. Stress syndrome in pigs is caused by a point mutation that replaces 1843CT in exon 17 of the ryanodine RYR1 receptor gene in a homozygous state. The aim of the study was to examine the genetic structure of individual pig populations at the locus of the RYR1 gene responsible for hypersensitivity. DNA testing of 102 pigs of Poltava meat, Myrhorod, Great White, Landrace and Pietren breeds was performed. The studies were performed on DNA samples obtained from pig blood. DNA was isolated using Chelex 100 reagent. Studies of the RYR1 gene fragment were performed by restriction fragment length polymorphism (RFPR) by polymerase chain reaction (PCR). Two alleles of the ryanodine RYR1 receptor gene (n and N) and three genotypes (NN, Nn, nn) were identified in the studied animals. A molecular study of pigs of different breeds revealed a polymorphism of the RYR1 gene. The number of animals carrying the recessive allele n of the ryanodine receptor gene RYR1, which is responsible for the sensitivity of pigs to stress factors, varied considerably: from its complete absence in the Vietnamese Pot-bellied, Ukrainian meat, Large White and Ukrainian Spotted Steppe breeds up to 100% of animals of homozygous RYR1nn genotype in the Piétrain breed and 50% of Landrace individuals with the heterozygous RYR1Nn genotype The mutant RYR1n allele was found in animals of the Piétrain breed with a 100% frequency. Heterozygous genotype RYR1Nn was found in pigs of Poltava Meat (10%), Landrace (50%), Myrhorod (15%) Ukrainian Spotted Steppe (50%). Homozygous RYR1NN genotype was detected in all Large White, Vietnamese Pot-bellied, and Ukrainian Meat pigs studied, indicating the absence of stress syndrome. It has been established that pigs of the Great White, Vietnamese Pot-bellied, and Ukrainian Meat breeds are preferred for breeding for biomedical purposes. Breeding of Piétrain pigs and any combinations with this breed makes it impossible to use such animals for biomedical experimental work.