Xenotransplantation means transplantation of organs and tissues from animals to human beings. Today, with use of new and more conventional immunosuppressive substances, it is possible to achieve good long-term survival of organs and cells transplanted between closely related species; for example, between baboon and man. However, large-scale treatment by xenotransplantation is still not possible because a transplantation between species such as pig and man will still not be successful. Nevertheless, many researchers have tried to solve these problems, and it is hoped that transgenic animals in combination with newer immunosuppressive treatment will make xenotransplantation a realistic possibility. The time horizon for clinically successful xenotransplantation with pig organs is unknown at the moment. Nevertheless, many investigators think that the breakthrough will occur in a few years time.