Xenotransplantation faces the dilemma of an unlimited supply of cells, tissues and organs on the one hand and severe obstacles and limits on the other. One reason for the limitations is that the source animal of choice, the pig, and the human recipient separated 90 million years ago during evolution, a time in which biological characteristics such as anatomy, physiology and immunology have had much time to drift far apart. The acceptance of such an evolutionary widely divergent organ, especially the heart of a pig, could evoke refusal of xenotransplantation in conservative and religious patients. New legal aspects of allocation of xenografts have therefore to be reflected upon and appropriate guidelines developed. Inquiries show, however, that the acceptance of all types of porcine organs would be high if the quality of life after receiving such a xenograft is comparable to that after receiving the same allograft. This individual benefit of a xenograft could lead to a disregard of the collective risk in terms of xenozoonoses, often presented as a catastrophic scenarium. Therefore, transplantation societies and ethics committees have published comments and even guidelines for handling future clinical xenotransplantation. All three monotheistic religions and Hinduism support the idea of saving and improving human life with the help of an animal organ. Copyrght (C) 2001 S. Karger AG, Basel.