Currently many efforts are being made to apply regenerative medicine to clinical renal diseases. It has
been suggested that some renal diseases which maintain renal structure can be treated by infusion of stem
cells isolated from the bone marrow or adult kidney. However such cell-based therapy cannot be applied
to the treatment of chronic renal disease, in which renal structure, including the kidney scaffold, is totally
disrupted. Therefore, absolute kidney regeneration is needed to rebuild a whole functional kidney de novo
and eliminate the requirement for dialysis. However, due to the anatomical complexity of the kidney and the
need for communication between each cell to fulfill renal function, the kidney has been labeled as the most
difficult organ to regenerate. Only a small number of  groups are investigating the potential for reconstructing
an organized and functional kidney structure, and, among them, we are using the developing xenoembryo
as an organ factory for this purpose. Here we review the challenges faced in developing a whole functional
kidney de novo and discuss the obstacles which must be overcome before clinical use is possible.