Advances are being made with the genetic engineering of pigs to make their organs adaptable for transplantation to humans. Hyperacute rejection mediated by anti–Gal&agr;(1,3)Gal antibodies can be avoided using transgenic pigs expressing a complement regulator. Most of this usually has been done with decay accelerating factor, but other regulators are under study. A major problem is vascular thrombosis, which occurs in 7 to 30 days in transgenic organs transplanted to primates. Work is proceeding to either produce a Gal knockout pig or remove Gal&agr;(1,3)Gal by other means. It is clear that pig organs can survive in primates for as long as 60 days, and at this time, there appear to be no hidden molecular incompatibilities.