Abstract
The expression of porcine endogenous retroviruses (PERV) was investigated in primary porcine peripheral blood leukocytes (PBL) of ten different pig breeds. The data suggest that PERV exists in all porcine PBL. A new retroviral element, a foamy‐like pol‐related sequence, was also detected in PBL. Three types of PERV were detected in almost every animal. The breeding of PERV‐free pigs is likely to be difficult. Further studies are required to assess the infectious disease risks associated with xenotransplantation.