Xenotransplantation has a history that dates far back into the 17th century. The first recorded instance of transplanting tissue from an animal into a human happened in 1682. In that year a portion of dog skull was implanted into the skull of a Russian nobleman to repair damage. The operation was seemingly a success, with no signs of rejection or infection. The operation was forced to be rescinded, however, after threats of excommunication from the Catholic Church. Thus arose not only the first successful xenotransplantation, but also the first ethical dilemma associated with the controversial medical procedure.

Over the course of the next two hundred years a few xenotransplantations were attempted, but most were performed in a simple trial and error manner. It was not until the early 1960s that the process became a systematic scientific study. In 1963 transplant pioneer Thomas Starzl transplanted baboon kidneys into six human patients. The recipients survived between 19 and 98 days. Later that same year Keith Reemtsma transplanted kidneys from chimpanzees into thirteen human patients. Most of the patients lived only a few days, but one did survive for nine months with no signs of organ rejection. His autopsy revealed he died of an electrolyte imbalance. The success of this operation instigated much more research into the nature and feasibility of xenotransplantation.

After the apparent successes of kidney xenotransplantation, doctors began to examine the possibilities of xenotransplanting other organs. In 1964 Hardy and colleagues from the University of Mississippi performed the first ever heart transplant. The donor was a chimp. The recipient was a 68-year-old man. He only lived for a matter of hours with his new heart. From 1969 to 1974 three children received livers from donor chimps. The children only survived from one to fourteen days, however. In 1984 came one of the most famous cases of xenotransplantation, the Baby Fae case. A newborn baby in California received a baboon heart. Using immunosuppressant drugs the baby lived twenty days. In 1992 the first successful liver xenotransplant was performed. Four different types of immunosuppressant drugs were used to help the patient survive for 71 days after the operation. He died of a brain hemorrhage. In 1992 the first recent successful non-primate xenotransplantation occurred when a pig liver was placed next to a patients own liver to buy time before a human donated liver could be found. The patient died after 32 hours.

So far no xenotransplantation has been considered completely successful. There are almost always complications arising from the human body's natural tendency to reject foreign entities. But with the advent of genetic engineering, science is continually advancing its methods and effectiveness with xenotransplantation. Since 1995 researchers have been genetically altering animal organs to be less prone to attack by the human body. In many cases the organs are attached to patient's circulation but kept outside of their bodies. Genetic research, coupled with advances in immunosuppressant drug therapy, makes the future of xenotransplantation bright. Continued research and investigation could one day lead to 100% successful operations.