Xenotransplantation may help to overcome the critical shortage of human tissues and organs for human transplantation, Swine represents an ideal source of such organs owing to their anatomical and physiological similarities to human besides their plentiful supply, However, the use of organs across the species barrier may be associated with the risk of transmission of pathogens, specially porcine endogenous retroviruses (PERVs).? Although most of these potential pathogens could be eliminated by pathogen-free breeding, PERVs are not eliminated by this treatment. PERVs are integrated into the genome of all pigs and produced by normal pig cells and infect human cells. They belong to gamma retroviruses and are of three classes viruses: A, B and C. In the present study, PCR based cloning was performed with chromosomal DNA extracted from pigs from domestic pigs in Korea. Amplified PCR fragments of about 1.5 Kb, covering the partial env gene, were cloned into pCR2.l-TOPO vectors and sequenced. A total of 91 env clones were obtained from domestic pigs, Berkshire, Duroc, Landrace and Yorkshire in Korea. Phylogenetic analysis of these genes revealed the presence of only PERV class A and B in the proportion of 58 % and 42 %, respectively. Among these, 28 clones had the correct open reading frame: 18 clones in class A and 10 clones in class B. Since both these PERV classes are polytropic and have the capacity to infect human cells, our data suggest that proviral PERVs have the potential to generate infectious viruses during or after xenotransplantation in human.