Abstract Already for some time the major histocompatibility system (MHS) is no longer considered to be only of importance in transplantation surgery. The MHS might also partly control specific immune responsiveness. In fact, tissue antigens may serve as a marker system for individual immunocompetence. So, in veterinary relevant species, tissue typing could be an important tool in breeding and health programs. The purpose of this review is to summarize the current knowledge of the MHS in different species.