Transplant, organ removed from one person and surgically implanted in another to replace a lost or diseased organ. Autotransplantation is the moving of an organ from one place to another within a person, where the original site has been affected by local disease (e.g., skin grafting). Blood transfusions between those with compatible blood groups was the first practical form of transplant. In organ transplantation, tissue compatibility typing as well as blood grouping are needed to minimize the risk of rejection. Immunosup-pressive drugs are also given to block the creation of antibodies that would attack the donor tissue. The most important, and now most successful, of organ transplants is that of the kidney. A single kidney is transplanted from a live donor who is a close relative or from a person who has recently suffered sudden death. Heart transplantation has been much publicized, but is limited to a few centers, and many problems remain. Liver and lung transplants have also been attempted, but there are still numerous difficulties. In corneal grafting the cornea of the eye of a recently dead person replaces that of a person with irreversible corneal damage leading to blindness. The lack of blood vessels in the cornea reduces the problem of rejection. Grafts from nonhuman animals are occasionally used (e.g., pig skin as temporary cover in extensive burns). Both animal and human heart valves are used in cardiac surgery.