As the number of patients waiting for matched organ donors increases, and as scientists find new ways of curbing transplant rejection, many researchers are looking at the transplantation of animal organs into humans in a more practical light. Yet, according to Frederick Murphy, professor of virology and dean of the UC Davis School of Veterinary Medicine, this process, known as "xenotransplantation," involves significant risk and will require careful regulation. Murphy encourages the development of public policy to coordinate oversight from the Centers for Disease Control and Prevention and the Food and Drug Administration. In an article in a recent issue of the journal Science, Murphy outlines what steps need to be taken in order to maximize communication among scientists and to minimize public health risks from viruses that could spread from species to species. In addition, Murphy addresses such issues as the use of baboon organs in transplantation, the phenomenon of highly resistant disease agents known as prions, and the fact that many animal substances such as bovine thyroid hormone and porcine heart valves are already used extensively in humans.