Cell therapy and tissue engineering may well likely dominate medical therapeutics in the next century. Growing a functional glomerular filter and tubule reabsorber from a combination of cells, biomaterials, and synthetic polymers to replace renal excretory and regulatory functions is a specific example of these evolving technologies. The kidney was the first organ whose function was substituted by an artificial device. The kidney was also the first organ to be successfully transplanted. The ability to replace renal function with these revolutionary technologies in the past was due to the fact that renal excretory function is based on natural physical forces which govern solute and fluid movement from the body compartment to the external environment. The need for coordinated mechanical or electrical activities got renal substitution was not required. Accordingly, the kidney may well be the first organ to be available as a tissue-engineered implantable device as a fully functional replacement part for the human body. The prospects of a "universal donor" bioartificial kidney for the treatment of end-stage renal disease are clearly achievable as we approach the next millennium.