The number of kidney transplantations performed per year is restricted by the limited availability of donor organs. One possible solution to this shortage is the use of renal xenografts. However, the transplantation of xenografts is complicated by hyperacute and acute rejection. A second possible solution is to ‘grow a kidney’ from a transplanted renal anlage. It has been postulated that the host immune response might be attenuated after the transplantation of such an anlage (metanephros) instead of a developed kidney. Transplanted metanephroi become chimeric organs in that their blood supply originates, at least partly, from the host. It is possible to transplant a developing metanephros, without the use of immunosuppression, from one rat to another. Transplanted metanephroi grow, differentiate, become vascularized, and function in host rats. ‘Growing kidneys’ via the transplantation of metanephroi may hold promise as a novel therapeutic approach to the treatment of chronic renal failure.