Sometime this year a human being is likely to receive a replacement organ from a pig genetically engineered for this purpose. It will not be the first time that animal organs have been used in an attempt to prolong human life. The first xenotransplantation procedures were conducted as early as 1964. So far, none can be considered successful - most recipients died within days, or even hours. The key problem is hyperacute rejection. This highly aggressive immune response can destroy the transplanted organ completely within minutes, and it cannot be controlled by immunosuppressive drugs. However, progress has been made. In this article,Inpharma® looks at research that has led to successful pig-to-monkey transplantations, and examines the implications of this research for future transplantation practice in humans.