The discovery of tissue stem cells has launched the current boom in the field of regenerative research, which is tremendously exciting and holds enormous therapeutic potential. However, despite such optimism, recent findings have tempered the potential for medical practice especially in case of anatomically complicated and functionally sophisticated organs such as kidney and lung. This article reviews recent findings on renal stem cells and their possible application in therapeutic intervention for acute renal failure, as well as the intensive attempts to build a functional kidney de novo for chronic renal failure, which may truly progress the next stage from "regenerative medicine" to "regenerative therapy".