We have previously shown that an approach called interspecies blastocyst complementation can be used to grow whole organs from pluripotent stem cells (PSCs) in an animal. The goal of this research is to alleviate the chronic shortage in donor organs for transplantation in cases of end-stage organ failure. Here, we demonstrate that this approach can be used to generate functional kidneys by growing mouse-PSC-derived kidneys in a rat. These studies provide proof-of-concept for generating human kidneys in animals, and a roadmap towards providing a reliable source of high-quality human kidneys for transplantation medicine.